Detailed entries for one subject from the INDEX TO HOW TO DO IT INFORMATION.
Click on a see also (sa) or tracing (xx) to view detailed entries about a related subject.
The entries are in alphabetical order by magazine name and then in chronological sequence.
To obtain a copy of any magazine article contact your local public library or the publisher.

The Twin-Twenty, Mark II. Construction details of a 20 watt (into 16 ohms) fully complementary silicon transistor power amplifier with automatic overload protection.
AUDIO AMATEUR 1/1970 [Winter 1970] (v.1#1) pg. 4
Added Info AUDIO AMATEUR 3/1970 [Summer 1970] (v.1#3) pg. 3
Added Info AUDIO AMATEUR 1/1971 (v.2#1) pg. 21
Added Info AUDIO AMATEUR 2/1971 [Nov 1971] (v.2#2) pg. 11, 14
Added Info AUDIO AMATEUR 3/1971 [Apr 1972] (v.2#3) pg. 21
Added Info AUDIO AMATEUR 2/1972 [Jan 1973] (v.3#2) pg. 18

Methods of protecting output transistors in audio amplifiers. Includes protection method limitations and a practical circuit providing a linear load-line characteristic.
AUDIO AMATEUR 3/1970 [Summer 1970] (v.1#3) pg. 11

The Bailey 30-30. A 30-watt (into 8-ohm load) stereo power amplifier has complementary PNP/NPN silicon output, overload protection, less than 0.1% THD at any level, and is unconditionally stable.
AUDIO AMATEUR 4/1970 [Fall 1970] (v.1#4) pg. 7, 11

Tip on changing the input capacitor on a JBL amplifier to eliminate ringing and improve bass transient response.
AUDIO AMATEUR 3/1971 [Apr 1972] (v.2#3) pg. 18

Tip on replacing some of the resistors in Southwest Technical Product's TIGER amplifier to protect it when operating at high power levels (approaching 80 watts).
AUDIO AMATEUR 1/1972 [Oct 1972] (v.3#1) pg. 27
Added Info AUDIO AMATEUR 2/1972 [Jan 1973] (v.3#2) pg. 18
Added Info AUDIO AMATEUR 1/1973 [Dec 1973] (v.4#1) pg. 29

The Edwin A+B amplifier. A new type of a true class-B amplifier with negligible cross-over distortion. With zero quiescent current through the output transistors and no special measures are needed for temperature stabilization.
AUDIO AMATEUR 3/1972 [Mar 1973] (v.3#3) pg. 3

Optimizing the Universal Tiger 175-A power amplifier to improve input protection, transient response and performance.
AUDIO AMATEUR 3/1972 [Mar 1973] (v.3#3) pg. 18

The super brute. 120 watt stereo amplifier is based on the 60-watt Dynaco Mark III circuit. It features independent power supplies for each channel, a very "stiff" B+ supply, an output tube DC balance adjustment, etc. Est. cost: $120.
AUDIO AMATEUR 3/1973 [Jul 1974] (v.4#3) pg. 11
Correction AUDIO AMATEUR 3/1974 [Feb 1975] (v.5#3) pg. 36
Added Info AUDIO AMATEUR 4/1974 [Apr 1975] (v.5#4) pg. 26

A power doubler. How to convert a pair of power amps into a large push/pull pair. Inverters allow your system to deliver twice the 4 Ohm power rating of your amplifier into 8 Ohm loads.
AUDIO AMATEUR 4/1973 [Aug 1974] (v.4#4) pg. 14

Modifying Southwest Technical's 175A Universal Tiger amplifier to produce 33% more amperage, but operate 20% cooler.
AUDIO AMATEUR 1/1974 [Oct 1974] (v.5#1) pg. 20

Report on constructing and testing the "Ampzilla" super power audio amplifier kit from Great American Sound Co. How to modify the unit for optimum performance.
AUDIO AMATEUR 2/1975 [Nov 1975] (v.6#2) pg. 11
Added Info AUDIO AMATEUR 1/1976 [May 1976] (v.7#1) pg. 24, 43
Added Info AUDIO AMATEUR 4/1976 [Dec 1976] (v.7#4) pg. 54
Added Info AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 48

A bilateral clipping indicator. This simple circuit will show instantly (on an LED) and in real-time whether an amplifier is being driven to clipping distortion (because it is being operated at too high a power level)
AUDIO AMATEUR 3/1975 [Jan 1976] (v.6#3) pg. 3
Added Info AUDIO AMATEUR 3/1977 [Aug 1977] (v.8#3) pg. 58
Added Info AUDIO AMATEUR 4/1978 [Nov 1978] (v.9#4) pg. 48

The Sanders electrostatic speaker and amplifier. A modified version of the Hermeyer electrostatic (issue 3/1972 and 4/1972). Part 2. Modification of the Hermeyer electrostatic amplifier, a smaller, lower-powered version.
AUDIO AMATEUR 1/1976 [May 1976] (v.7#1) pg. 12
Added Info AUDIO AMATEUR 2/1976 [Jul 1976] (v.7#2) pg. 39 (AR amplifier)
Correction AUDIO AMATEUR 3/1976 [Oct 1976] (v.7#3) pg. 39

Classic circuitry. Schematic of the D-76 amplifier from Audio Research Corp. (circa 1974).
AUDIO AMATEUR 1/1976 [May 1976] (v.7#1) pg. 36

Report on assembling the Heath basic power amplifier kit model AA-1640.
AUDIO AMATEUR 2/1976 [Jul 1976] (v.7#2) pg. 10
Correction AUDIO AMATEUR 4/1976 [Dec 1976] (v.7#4) pg. 50

Optimum performance from high-power amplifiers. A look at the dependence of amplifier performance upon AC power line voltage.
AUDIO AMATEUR 2/1976 [Jul 1976] (v.7#2) pg. 26
Added Info AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 38

Classic circuitry. Schematic for the Marantz model 2 power amplifier.
AUDIO AMATEUR 2/1976 [Jul 1976] (v.7#2) pg. 38
Correction AUDIO AMATEUR 3/1976 [Oct 1976] (v.7#3) pg. 39

Improving the ventilation of the Dynaco Stereo 70 amplifier will increase tube life.
AUDIO AMATEUR 3/1976 [Oct 1976] (v.7#3) pg. 34

Dynaco's Stereo 70 amplifier. A simple modification to refurbish the chassis, upgrade the power supply, improve the bias supply, etc.
AUDIO AMATEUR 4/1976 [Dec 1976] (v.7#4) pg. 13
Correction AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 47
Added Info AUDIO AMATEUR 1/1979 [Feb 1979] (v.10#1) pg. 55

Slewing induced distortion (SID) in audio amplifiers. Part 1.
AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 4

Updating an early Dynaco ST-120 power amplifier.
AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 34

Classic circuitry. Schematic of the Marantz model 9 power amplifier.
AUDIO AMATEUR 1/1977 [Feb 1977] (v.8#1) pg. 44

Transient response (a do-it-yourself clinic). Practical solutions for your system to make recorded music sound more like live music. Looks at cartridge, preamp, amplifier, speakers, etc.
AUDIO AMATEUR 2/1977 [May 1977] (v.8#2) pg. 12

Report on assembling the Stereo 400 power amplifier kit from Dynaco. How to realize maximum performance from the finished kit. Includes the "Double 400" modifications.
AUDIO AMATEUR 2/1977 [May 1977] (v.8#2) pg. 48
Correction AUDIO AMATEUR 4/1977 [Dec 1977] (v.8#4) pg. 51

A summary of the reports on four kit-built super power amplifiers (GAS Ampzilla, Heath AA-1640, Dynaco Stereo 400, and Dynaco Double 400).
AUDIO AMATEUR 2/1977 [May 1977] (v.8#2) pg. 62

A high efficiency electrostatic loudspeaker system. Part 2. New design power amplifier to drive the speakers.
AUDIO AMATEUR 3/1977 [Aug 1977] (v.8#3) pg. 8
Correction AUDIO AMATEUR 3/1978 [Sep 1978] (v.9#3) pg. 54
Added Info AUDIO AMATEUR 4/1979 [Oct 1979] (v.10#4) pg. 63
Added Info AUDIO AMATEUR 4/1987 [Nov 1987] (v.18#4) pg. 49

Classic circuitry. Basic schematics for the JC-2 amplifier (circa 1973-1976).
AUDIO AMATEUR 3/1977 [Aug 1977] (v.8#3) pg. 48
Added Info AUDIO AMATEUR 1/1978 [Mar 1978] (v.9#1) pg. 67
Correction AUDIO AMATEUR 2/1978 [Jun 1978] (v.9#2) pg. 49
Added Info AUDIO AMATEUR 4/1978 [Nov 1978] (v.9#4) pg. 50
Added Info AUDIO AMATEUR 1/1980 [Jan 1980] (v.11#1) pg. 57

Audio Research remakes Dynaco's Stereo 70. How to convert your Stereo 70 to an AR style amplifier that is a lower powered version of the AR D-76-A (30 watts per channel).
AUDIO AMATEUR 4/1977 [Dec 1977] (v.8#4) pg. 4

Classic circuitry. Schematic of the D-76A amplifier from Audio Research Corp. (circa 1975).
AUDIO AMATEUR 4/1977 [Dec 1977] (v.8#4) pg. 50

Modifying the Scott LK150 amplifier to use RCA 8417 beam power tubes in place of more expensive 6550 tubes.
AUDIO AMATEUR 1/1978 [Mar 1978] (v.9#1) pg. 46

Classic circuitry. Schematic of the Marantz power amplifier model 5.
AUDIO AMATEUR 1/1978 [Mar 1978] (v.9#1) pg. 62

Simple way to reduce crosstalk and help prevent clipping on transients in a normal stereo amplifier or preamp.
AUDIO AMATEUR 2/1978 [Jun 1978] (v.9#2) pg. 42

Classic circuitry. Ulric J. Child's model 505A 50 watt class A amplifier (circa 1950).
AUDIO AMATEUR 3/1978 [Sep 1978] (v.9#3) pg. 47

The Nelson Pass A40 power amplifier (40 watts per channel Class A).
AUDIO AMATEUR 4/1978 [Nov 1978] (v.9#4) pg. 4
Correction AUDIO AMATEUR 1/1979 [Feb 1979] (v.10#1) pg. 50
Added Info AUDIO AMATEUR 2/1979 [Apr 1979] (v.10#2) pg. 49
Correction AUDIO AMATEUR 3/1980 [Jun 1980] (v.11#3) pg. 50
Added Info AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 49
Added Info AUDIO AMATEUR 3/1986 [Aug 1986] (v.17#3) pg. 53
Added Info AUDIO AMATEUR 3/1987 [Jul 1987] (v.18#3) pg. 54
Added Info AUDIO AMATEUR 2/1988 [May 1988] (v.19#2) pg. 59
Added Info AUDIO AMATEUR 4/1989 [Oct 1989] (v.20#4) pg. 61
Added Info AUDIO AMATEUR 3/1990 [Aug 1990] (v.21#3) pg. 45
Added Info AUDIO AMATEUR 2/1992 [Jun 1992] (v.23#2) pg. 56
Added Info SPEAKER BUILDER 6/1992 [Dec 1992] (v.13#6) pg. 46
Added Info AUDIO ELECTRONICS 6/1998 [Dec 1998] (v.29#6) pg. 43
Added Info AUDIOXPRESS Jun 2001 (v.32#6) pg. 76 (Updated parts list)

(1) Interchangeability of the 6550 tube and the KT88 tube in audio amplifiers is questioned. (2) Substitutes for 6550 tubes noted.
AUDIO AMATEUR 4/1978 [Nov 1978] (v.9#4) pg. 52
Added Info AUDIO AMATEUR 2/1979 [Apr 1979] (v.10#2) pg. 37, 48

Mark III microfarads multiplied. Simple and inexpensive modifications to Dynaco Mark IIIs include adding 500uF of capacitance on either side of the B+ filter choke.
AUDIO AMATEUR 1/1979 [Feb 1979] (v.10#1) pg. 34

Modifying a David Hermeyer ESA-3 amplifier to operate at a B+ of 2200VDC. This direct coupled amplifier will then be capable of driving a .062" diaphragm-to-stator spaced electrostatic speaker.
AUDIO AMATEUR 1/1979 [Feb 1979] (v.10#1) pg. 40

Classic circuitry. Schematic for the Marantz 8B power amplifier.
AUDIO AMATEUR 2/1979 [Apr 1979] (v.10#2) pg. 20

The Williamson 40/40 power amplifier. Construction details of a 40 watt stereo amplifier (into 8 ohm loading).
AUDIO AMATEUR 4/1979 [Oct 1979] (v.10#4) pg. 5
Correction AUDIO AMATEUR 1/1980 [Jan 1980] (v.11#1) pg. 56
Correction AUDIO AMATEUR 3/1980 [Jun 1980] (v.11#3) pg. 50
Added Info AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 47

Tip on always using the 4-ohm speaker tap on a Dynaco Mark III.
AUDIO AMATEUR 4/1979 [Oct 1979] (v.10#4) pg. 55
Added Info AUDIO AMATEUR 1/1980 [Jan 1980] (v.11#1) pg. 62

Test report on the Hafler DH-200 power amplifier, available in both kit and wired form.
AUDIO AMATEUR 2/1980 [Mar 1980] (v.11#2) pg. 38
Added Info AUDIO AMATEUR 1/1981 [Feb 1981] (v.12#1) pg. 50

Classic circuitry. Schematic for McIntosh Laboratories' MC-60 type A-121 power amplifier (circa 1956).
AUDIO AMATEUR 3/1980 [Jun 1980] (v.11#3) pg. 48

Test report on the Heath AA-1600 stereo power amplifier kit.
AUDIO AMATEUR 4/1980 [Nov 1980] (v.11#4) pg. 56
Added Info AUDIO AMATEUR 1/1981 [Feb 1981] (v.12#1) pg. 42, 48

An input amplifier bypass modification for the Heathkit AA-1640 amplifier.
AUDIO AMATEUR 1/1981 [Feb 1981] (v.12#1) pg. 39

Build a MOSFET Citation 12. Update the Harman Kardon Citation 12 audio amplifier by installing International Rectifier's IRF 130 power mosfets which have advantages over regular bipolar transistors in audio power amplifier use.
AUDIO AMATEUR 2/1981 [Apr 1981] (v.12#2) pg. 6
Correction AUDIO AMATEUR 4/1981 [Sep 1981] (v.12#4) pg. 57
Added Info AUDIO AMATEUR 2/1983 [Jun 1983] (v.14#2) pg. 36

The ST-150-BJ-1. A Boak-Jung modification of the Dynaco Stereo 150 amplifier. Changes include (1) capacitors, (2) power supply and output wiring, (3) power regulation, and (4) upgrading components.
AUDIO AMATEUR 2/1981 [Apr 1981] (v.12#2) pg. 32, 40
Correction AUDIO AMATEUR 4/1981 [Sep 1981] (v.12#4) pg. 57
Added Info AUDIO AMATEUR 3/1986 [Aug 1986] (v.17#3) pg. 49

Classic circuitry. Schematic for John Curl's JC-3 power amplifier.
AUDIO AMATEUR 2/1981 [Apr 1981] (v.12#2) pg. 56

Merits and mathematics of bi-amplification are discussed.
AUDIO AMATEUR 2/1981 [Apr 1981] (v.12#2) pg. 65
Added Info AUDIO AMATEUR 4/1981 [Sep 1981] (v.12#4) pg. 59

Classic circuitry. Schematic of the McIntosh model MC-30, Type A-116B power amplifier (circa 1956).
AUDIO AMATEUR 3/1981 [Jun 1981] (v.12#3) pg. 47

POOGE-2. A modification "symphony" for your Hafler DH-200 or other power amplifiers. Looks at electrical contacts, wiring, capacitors, etc.
AUDIO AMATEUR 4/1981 [Sep 1981] (v.12#4) pg. 7
Added Info AUDIO AMATEUR 1/1982 [Jan 1982] (v.13#1) pg. 56, 57
Added Info AUDIO AMATEUR 2/1982 [May 1982] (v.13#2) pg. 55
Added Info AUDIO AMATEUR 1/1983 [Apr 1983] (v.14#1) pg. 55
Added Info AUDIO AMATEUR 4/1983 [Nov 1983] (v.14#4) pg. 55
Added Info AUDIO AMATEUR 1/1987 [Jan 1987] (v.18#1) pg. 54

Classic circuitry. Schematics of the (1) Acrosound 100 watt amplifier with the TO-350 transformer and (2) power supply for 100 watt ultra-linear amplifier. (Circa 1960).
AUDIO AMATEUR 4/1981 [Sep 1981] (v.12#4) pg. 56

Classic circuitry. Marantz Audio Consolette mono amplifier.
AUDIO AMATEUR 1/1982 [Jan 1982] (v.13#1) pg. 51

Basics of vacuum tube audio amplifier design and construction.
AUDIO AMATEUR 1/1982 [Jan 1982] (v.13#1) pg. 55
Correction AUDIO AMATEUR 2/1982 [May 1982] (v.13#2) pg. 50

A 60W MOSFET power amplifier.
AUDIO AMATEUR 2/1982 [May 1982] (v.13#2) pg. 7
Correction AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 48, 54
Added Info AUDIO AMATEUR 3/1984 [Jul 1984] (v.15#3) pg. 40
Added Info AUDIO AMATEUR 2/1985 [Mar 1985] (v.16#2) pg. 49
Added Info AUDIO AMATEUR 3/1985 [Jul 1985] (v.16#3) pg. 56
Added Info AUDIO AMATEUR 3/1989 [Aug 1989] (v.20#3) pg. 39
Added Info AUDIO AMATEUR 1/1992 [Mar 1992] (v.23#1) pg. 62
Added Info AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 9, 38
Added Info AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 20
Added Info AUDIO AMATEUR 1/1994 [Mar 1994] (v.25#1) pg. 30

Classic circuitry. Schematic for the Audio Research Corp. D-51 amplifier (circa 1973).
AUDIO AMATEUR 2/1982 [May 1982] (v.13#2) pg. 49

Modifications for Southwest Technical's 198A Preamp, 207 Power Amp, and 210 Power Amp are suggested.
AUDIO AMATEUR 2/1982 [May 1982] (v.13#2) pg. 50
Added Info AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 50
Correction AUDIO AMATEUR 4/1982 [Oct 1982] (v.13#4) pg. 54

DC servo loop design for audio amplifiers. How servo loops work and how they help eliminate capacitor distortion problems.
AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 14
Correction AUDIO AMATEUR 5/1982 [Jan 1983] (v.13#5) pg. 53
Added Info AUDIO AMATEUR 5/1982 [Jan 1983] (v.13#5) pg. 54, 55

Improvements for Hafler's DH-101 preamplifier and two power amplifiers (DH-200 and DH-500).
AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 32
Added Info AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 56

Kit report on the Heath AA-1800 stereo power amplifier.
AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 42

Classic circuitry. Schematic of the Quad II control unit (preamp) and main amplifier.
AUDIO AMATEUR 3/1982 [Aug 1982] (v.13#3) pg. 47

Classic circuitry. Schematic for a transformerless tube-type 25W amplifier. (circa 1954).
AUDIO AMATEUR 5/1982 [Jan 1983] (v.13#5) pg. 49
Added Info AUDIO AMATEUR 1/1983 [Apr 1983] (v.14#1) pg. 56, 57
Added Info AUDIO AMATEUR 3/1983 [Sep 1983] (v.14#3) pg. 54
Added Info AUDIO AMATEUR 4/1983 [Nov 1983] (v.14#4) pg. 56

Classic circuitry. Schematic for the Fisher Laboratory Standard Amplifier, model 50-AZ.
AUDIO AMATEUR 1/1983 [Apr 1983] (v.14#1) pg. 40

Improving the Hafler DH-500 amplifier kit through added cooling, improved wiring and connectors, etc.
AUDIO AMATEUR 2/1983 [Jun 1983] (v.14#2) pg. 18
Added Info AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 56

Test report on the Radio Systems PW-200 solid state power amplifier kit.
AUDIO AMATEUR 2/1983 [Jun 1983] (v.14#2) pg. 40

Troubleshooting protection circuits in transistorized audio amplifiers.
AUDIO AMATEUR 2/1983 [Jun 1983] (v.14#2) pg. 46

Modify your Dynaco Stereo 400 amplifier.
AUDIO AMATEUR 3/1983 [Sep 1983] (v.14#3) pg. 21
Added Info AUDIO AMATEUR 5/1984 [Oct 1984] (v.15#5) pg. 58

Test report on the Fujitech A501 amplifier kit.
AUDIO AMATEUR 3/1983 [Sep 1983] (v.14#3) pg. 50

New power amp alternatives (in high-quality audio power amplifier design). A 200 watt version. Part 1. Overall system setup, the main amplifier circuits and the auxiliary cascode amplifier.
AUDIO AMATEUR 4/1983 [Nov 1983] (v.14#4) pg. 7
Added Info AUDIO AMATEUR 4/1988 [Oct 1988] (v.19#4) pg. 63

Classic circuitry. Schematic for the Mullard 5-20 high quality amplifier.
AUDIO AMATEUR 4/1983 [Nov 1983] (v.14#4) pg. 50

New devices for audio from National Semiconductor. Circuits included for a differential amplifier, operational amplifier, phono preamp, line level amp, etc.
AUDIO AMATEUR 5/1983 [Jan 1984] (v.14#5) pg. 7
Added Info AUDIO AMATEUR 1/1985 [Jan 1985] (v.16#1) pg. 55

New power amp alternatives (in high-quality audio power amplifier design). A 200 watt version. Part 2. Power monitor, power supply, and construction hints.
AUDIO AMATEUR 5/1983 [Jan 1984] (v.14#5) pg. 30
Correction AUDIO AMATEUR 1/1985 [Jan 1985] (v.16#1) pg. 53

Third-generation MOSFET power amplifiers. Part 1. The Servo 100. A 100 watt audio power amplifier featuring rack panels, large end-mounted heat sinks, compact toroidal transformer and separate pairs of filter capacitors for each channel.
AUDIO AMATEUR 1/1984 [Mar 1984] (v.15#1) pg. 7
Added Info AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 54
Added Info AUDIO AMATEUR 2/1986 [May 1986] (v.17#2) pg. 48
Added Info AUDIO AMATEUR 2/1987 [Mar 1987] (v.18#2) pg. 40
Added Info AUDIO AMATEUR 2/1989 [Apr 1989] (v.20#2) pg. 50, 52
Added Info AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 9
Added Info AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 20
Added Info AUDIO AMATEUR 3/1994 [Sep 1994] (v.25#3) pg. 36

New power amp alternatives (in high-quality audio power amplifier design). A 200 watt version. Part 3. An audio activated power switch.
AUDIO AMATEUR 1/1984 [Mar 1984] (v.15#1) pg. 35

Classic circuitry. Schematic for the Heathkit Model W-6M 70W amplifier.
AUDIO AMATEUR 1/1984 [Mar 1984] (v.15#1) pg. 44
Added Info AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 52 (Modifications)

Third-generation MOSFET power amplifiers. Part 2. The DC 100. A DC-coupled 100W audio amplifier.
AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 13
Added Info AUDIO AMATEUR 1/1985 [Jan 1985] (v.16#1) pg. 54
Added Info AUDIO AMATEUR 2/1985 [Mar 1985] (v.16#2) pg. 50
Added Info AUDIO AMATEUR 3/1989 [Aug 1989] (v.20#3) pg. 42
Correction AUDIO AMATEUR 1/1991 [Feb 1991] (v.22#1) pg. 55
Added Info AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 9
Added Info AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 20

Classic circuitry. Schematic for the Audio Research Corp. D-150 amplifier (circa 1975).
AUDIO AMATEUR 2/1984 [May 1984] (v.15#2) pg. 44

Ampzilla III. An updated version of the solid-state, 200W/channel amplifier that first appeared in Popular Electronics (Oct 1974).
AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 7
Added Info AUDIO AMATEUR 1/1985 [Jan 1985] (v.16#1) pg. 53
Correction AUDIO AMATEUR 2/1985 [Mar 1985] (v.16#2) pg. 48
Added Info AUDIO AMATEUR 2/1988 [May 1988] (v.19#2) pg. 53
Added Info AUDIO AMATEUR 2/1991 [Apr 1991] (v.22#2) pg. 65
Added Info AUDIO AMATEUR 3/1992 [Sep 1992] (v.23#3) pg. 40
Added Info AUDIO AMATEUR 2/1993 [Jun 1993] (v.24#2) pg. 39

Four-speed automatic fan control for an audio amplifier. Controls the fan speed in proportion to heat sink temperature.
AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 24

Classic circuitry. Schematic of the Lowther 26W LL26 amplifier.
AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 49

Report on the MKH-200C kit for modifying the Hafler DH-200 amplifier.
AUDIO AMATEUR 4/1984 [Sep 1984] (v.15#4) pg. 50

Classic circuitry. Schematic for the Leak preamplifier and power amplifier (circa 1952).
AUDIO AMATEUR 5/1984 [Oct 1984] (v.15#5) pg. 48

The sound of amplifiers. How to choose the "right" amplifier for a particular listening environment.
AUDIO AMATEUR 3/1985 [Jul 1985] (v.16#3) pg. 6
Correction AUDIO AMATEUR 4/1985 [Oct 1985] (v.16#4) pg. 54
Added Info AUDIO AMATEUR 1/1986 [Feb 1986] (v.17#1) pg. 50, 54
Added Info AUDIO AMATEUR 3/1986 [Aug 1986] (v.17#3) pg. 52

Low-distortion, low-feedback power amplifiers. Modifications for the BES model 850 (forerunner of the Streets model 950).
AUDIO AMATEUR 3/1985 [Jul 1985] (v.16#3) pg. 24

Defects in amplifier performance. Reprint of a 1957 article dealing with audible distortion.
AUDIO AMATEUR 4/1985 [Oct 1985] (v.16#4) pg. 26

Report on the Fujitech A-1033 integrated tube amplifier kit which combines a full-function preamp and a 15W (or 30W) amplifier in one chassis.
AUDIO AMATEUR 4/1985 [Oct 1985] (v.16#4) pg. 46
Added Info AUDIO AMATEUR 4/1986 [Oct 1986] (v.17#4) pg. 55

The Lang 20W class-A MOSFET amplifier. A complete 20W single channel amp is contained on a single 6"x6" circuit board.
AUDIO AMATEUR 2/1986 [May 1986] (v.17#2) pg. 7
Added Info AUDIO AMATEUR 4/1987 [Nov 1987] (v.18#4) pg. 58
Added Info AUDIO AMATEUR 1/1988 [Feb 1988] (v.19#1) pg. 51
Correction AUDIO AMATEUR 2/1988 [May 1988] (v.19#2) pg. 48

Tip on upgrading capacitors in older audio amplifiers.
AUDIO AMATEUR 2/1986 [May 1986] (v.17#2) pg. 39

Classic circuitry. Schematic for the Jefferson 2A3 amplifier circuit (circa 1933).
AUDIO AMATEUR 2/1986 [May 1986] (v.17#2) pg. 45

A 500W MOSFET power amplifier. Complete construction details for a 1.1kW stereo output stage with all the professional power amplifier features. Part 1. The power module.
AUDIO AMATEUR 4/1986 [Oct 1986] (v.17#4) pg. 17

A 500W MOSFET power amplifier. Part 2. Soft start switching circuit.
AUDIO AMATEUR 1/1987 [Jan 1987] (v.18#1) pg. 15
Added Info AUDIO AMATEUR 4/1988 [Oct 1988] (v.19#4) pg. 50

Simple biasing SCC (symmetrical complimentary configuration) amplifier circuit.
AUDIO AMATEUR 1/1987 [Jan 1987] (v.18#1) pg. 44
Correction AUDIO AMATEUR 4/1987 [Nov 1987] (v.18#4) pg. 50

Classic circuitry. Schematic of D.T.N. Williamson's power amplifier (circa 1947).
AUDIO AMATEUR 3/1987 [Jul 1987] (v.18#3) pg. 49

Classic circuitry. Schematic of the GAS Ampzilla Grandson (circa 1977).
AUDIO AMATEUR 1/1988 [Feb 1988] (v.19#1) pg. 46

A 40W all-MOSFET power amp. Part 1.
AUDIO AMATEUR 2/1988 [May 1988] (v.19#2) pg. 7
Added Info AUDIO AMATEUR 3/1988 [Aug 1988] (v.19#3) pg. 52
Added Info AUDIO AMATEUR 1/1989 [Feb 1989] (v.20#1) pg. 56
Added Info AUDIO AMATEUR 2/1989 [Apr 1989] (v.20#2) pg. 46
Added Info AUDIO AMATEUR 2/1990 [Apr 1990] (v.21#2) pg. 4
Added Info AUDIO AMATEUR 3/1995 [Aug 1995] (v.26#3) pg. 47

Classic Circuitry. Schematic diagrams of three power amps from Triad Transformer Co. (circa 1950). (1) Transformer-coupled amplifier. (2) Williamson amplifier. (3) 18W Kappler amplifier.
AUDIO AMATEUR 2/1988 [May 1988] (v.19#2) pg. 46

A 40W all-MOSFET power amp. Part 2.
AUDIO AMATEUR 3/1988 [Aug 1988] (v.19#3) pg. 35
Correction AUDIO AMATEUR 2/1989 [Apr 1989] (v.20#2) pg. 50
Added Info AUDIO AMATEUR 3/1989 [Aug 1989] (v.20#3) pg. 53
Added Info AUDIO AMATEUR 4/1992 [Dec 1992] (v.23#4) pg. 40

The DC300B tube MOSFET amplifier. Combines a high-quality tube driver with a very fast MOSFET current amplifier. Usable with low impedance speakers. Part 1.
AUDIO AMATEUR 1/1989 [Feb 1989] (v.20#1) pg. 14

The DC300B tube MOSFET amplifier. Part 2.
AUDIO AMATEUR 2/1989 [Apr 1989] (v.20#2) pg. 16
Added Info AUDIO AMATEUR 4/1989 [Oct 1989] (v.20#4) pg. 56
Added Info AUDIO AMATEUR 2/1990 [Apr 1990] (v.21#2) pg. 66
Correction AUDIO AMATEUR 2/1990 [Apr 1990] (v.21#2) pg. 68
Added Info AUDIO AMATEUR 3/1991 [Aug 1991] (v.22#3) pg. 48
Added Info AUDIO AMATEUR 4/1991 [Oct 1991] (v.22#4) pg. 52

Classic circuitry. Schematic of the Grommes G101 power amp (circa 1964).
AUDIO AMATEUR 3/1989 [Aug 1989] (v.20#3) pg. 49

Feedforward error cancellation. Principles and design for an older (circa 1929) form of error correction to improve some amplifier distortion and noise problems. Part 1. Basic theory and how to apply it to a line amplifier.
AUDIO AMATEUR 4/1989 [Oct 1989] (v.20#4) pg. 15

Explanation of the impact on amplifiers when changing from an 8-ohm load to a 4-ohm load.
AUDIO AMATEUR 4/1989 [Oct 1989] (v.20#4) pg. 43

Feedforward error cancellation. Part 1. Principles and design for a high-quality feedforward radio frequency (RF) line amplifier.
AUDIO AMATEUR 4/1989 [Oct 1989] (v.20#4) pg. 15

Taming the flaming Tyger. Restoration of a Southwest Technical Products Corp. (SWTPC) Model 210/A Tigersaurus audio amplifier. Part 1.
AUDIO AMATEUR 1/1990 [Feb 1990] (v.21#1) pg. 26
Added Info AUDIO AMATEUR 4/1990 [Oct 1990] (v.21#4) pg. 59

Taming the flaming Tyger. Restoration of a Southwest Technical Products Corp. (SWTPC) Model 210/A Tigersaurus audio amplifier. Part 2.
AUDIO AMATEUR 2/1990 [Apr 1990] (v.21#2) pg. 32
Correction AUDIO AMATEUR 3/1990 [Aug 1990] (v.21#3) pg. 5
Added Info AUDIO AMATEUR 3/1990 [Aug 1990] (v.21#3) pg. 60

A multi-tone intermodulation meter. Part 3. Measuring nonlinear distortions. Applying the IM (intermodulation) meter measurements to existing amplifiers and proposed improvements to amplifier design.
AUDIO AMATEUR 3/1990 [Aug 1990] (v.21#3) pg. 8
Added Info AUDIO AMATEUR 2/1991 [Apr 1991] (v.22#2) pg. 32

Restoring the Dynaco SCA-80Q for use as a premium amplifier for a small system.
AUDIO AMATEUR 3/1990 [Aug 1990] (v.21#3) pg. 47
Added Info AUDIO AMATEUR 2/1991 [Apr 1991] (v.22#2) pg. 70

An easy circuit to protect your audio amplifier from a low impedance (short circuit) before the amp is connected to the load.
AUDIO AMATEUR 4/1990 [Oct 1990] (v.21#4) pg. 44

Tips on POOGE-ing (improving) a Heath AA1500 basic power amplifier.
AUDIO AMATEUR 4/1990 [Oct 1990] (v.21#4) pg. 59

Balanced audio amplifiers. How to use balanced topology in your equipment. Many practical circuits shown.
AUDIO AMATEUR 1/1991 [Feb 1991] (v.22#1) pg. 14
Added Info AUDIO AMATEUR 2/1991 [Apr 1991] (v.22#2) pg. 65
Added Info AUDIO AMATEUR 3/1991 [Aug 1991] (v.22#3) pg. 38
Added Info AUDIO AMATEUR 1/1992 [Mar 1992] (v.23#1) pg. 54
Added Info AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 46
Added Info AUDIO AMATEUR 1/1994 [Mar 1994] (v.25#1) pg. 44

Classic circuitry. Schematic of the Bell model 2200B high-fidelity amplifier (circa 1953).
AUDIO AMATEUR 1/1991 [Feb 1991] (v.22#1) pg. 53

Feedforward error cancellation. Part 2. How to use the right components to implement the line amplifier, results of some distortion-cancelling experiments, and a complete line-amplifier design (including a parts list).
AUDIO AMATEUR 3/1991 [Aug 1991] (v.22#3) pg. 10
Added Info AUDIO AMATEUR 2/1992 [Jun 1992] (v.23#2) pg. 52

A 35W power amplifier from salvaged parts (from a Dynaco ST-70) is both visually and audibly competitive to commercial high tech power amplifiers.
AUDIO AMATEUR 1/1992 [Mar 1992] (v.23#1) pg. 9

MOSFET mod for the Dynaco ST-120. Stock 60W/channel amplifier circuit boards and wiring are replaced with new boards that deliver about 90W/channel with 4-ohm loads. Est. cost: $100.
AUDIO AMATEUR 3/1992 [Sep 1992] (v.23#3) pg. 14
Correction AUDIO AMATEUR 2/1993 [Jun 1993] (v.24#2) pg. 38
Added Info AUDIO ELECTRONICS 2/1999 [Mar 1999] (v.30#2) pg. 22 (Updated mod using currently available parts)
Added Info AUDIOXPRESS Nov 2001 (v.32#11) pg. 83 (Updated mod parts souce)

Build the A75 power amplifier. The Nelson Pass A40 design is modified and updated. Part 1. How and why of the design decisions and some of the alternatives.
AUDIO AMATEUR 4/1992 [Dec 1992] (v.23#4) pg. 9
Added Info AUDIOXPRESS Nov 2002 (v.33#11) pg. 6 (Improved design. Part 1)
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 6 (Improved design. Part 2)

Build the A75 power amplifier. The Nelson Pass A40 design is modified and updated. Part 2. In depth analysis of the amplifier's component parts (power supply and front end). Includes schematics, PC board layouts, and parts lists.
AUDIO AMATEUR 1/1993 [Mar 1993] (v.24#1) pg. 20
Correction AUDIO AMATEUR 2/1993 [Jun 1993] (v.24#2) pg. 38, 39
Correction AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 37
Added Info AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 37
Added Info AUDIO AMATEUR 4/1995 [Nov 1995] (v.26#4) pg. 44
Added Info GLASS AUDIO 5/1996 (v.8#5) pg. 62
Added Info AUDIO ELECTRONICS 4/1999 [Aug 1999] (v.30#4) pg. 34
Added Info AUDIOXPRESS Jun 2001 (v.32#6) pg. 82

The FET-80 power amp. Philosophy and circuit design for a high-quality audio power amplifier that uses low-cost, solid-state topology.
AUDIO AMATEUR 2/1993 [Jun 1993] (v.24#2) pg. 8
Correction AUDIO AMATEUR 3/1993 [Sep 1993] (v.24#3) pg. 37
Correction AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 44
Added Info AUDIO AMATEUR 2/1994 [Jun 1994] (v.25#2) pg. 38

Classic circuitry. Schematic for the GEC 88-50 50W amplifier (circa 1957).
AUDIO AMATEUR 4/1993 [Dec 1993] (v.24#4) pg. 36

Optimizing Borbely's EB-60W power amplifier. Changes include a linear regulator for the power supply, soft start, and EMI/RFI filter.
AUDIO AMATEUR 1/1994 [Mar 1994] (v.25#1) pg. 30

Classic circuitry. Schematic for the Ampzilla II
AUDIO AMATEUR 1/1994 [Mar 1994] (v.25#1) pg. 42

The Pass Zen amplifier. Instructions for building a simple 10 watt single-stage single-ended Class A MOSFET amplifier. Part 1.
AUDIO AMATEUR 2/1994 [Jun 1994] (v.25#2) pg. 10
Added Info AUDIO AMATEUR 3/1994 [Sep 1994] (v.25#3) pg. 47
Added Info AUDIO AMATEUR 4/1994 [Dec 1994] (v.25#4) pg. 47, 48
Added Info AUDIO AMATEUR 3/1996 [Sep 1996] (v.27#3) pg. 40
Added Info AUDIO ELECTRONICS 2/1997 [Apr 1997] (v.28#2) pg. 44
Added Info AUDIO ELECTRONICS 4/1998 [Aug 1998] (v.29#4) pg. 30
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 16

The Pass Zen amplifier. Part 2. Upgrades.
AUDIO AMATEUR 3/1994 [Sep 1994] (v.25#3) pg. 20

On amplifiers and feedback. An examination of various feedback strategies and feedback claims of commercial amplifiers.
AUDIO AMATEUR 1/1995 [Jan 1995] (v.26#1) pg. 20

Toward an all-digital power amplifier. A look at the major components which make up a proposed digital power amplifier (or PCM-to-PWM converter).
AUDIO AMATEUR 2/1995 [Jun 1995] (v.26#2) pg. 36
Added Info AUDIO AMATEUR 4/1995 [Nov 1995] (v.26#4) pg. 51

Report on the Marchand PM2 power amplifier kit and PS11 dual 40V power supply. Includes construction tips and specifications.
AUDIO AMATEUR 3/1995 [Aug 1995] (v.26#3) pg. 42

On power amplifier feedback networks. An examination of two popular feedback network topologies looks at the problems and advantages of each. How to switch networks in your power amplifier to improve operation.
AUDIO AMATEUR 1/1996 [Mar 1996] (v.27#1) pg. 12

10W Class A amplifier features moderate cost and high quality. The heat sinks and power supplies are of reasonable size and cost. Est. cost: $150.
AUDIO AMATEUR 3/1996 [Sep 1996] (v.27#3) pg. 22
Correction AUDIO ELECTRONICS 4/1996 [Dec 1996] (v.27#4) pg. 39
Correction AUDIO ELECTRONICS 2/1997 [Apr 1997] (v.28#2) pg. 32
Added Info AUDIO ELECTRONICS 5/1999 [Sep 1999] (v.30#5) pg. 54

Son of Zen. An improved version of the Nelson Pass "Zen Amplifier" features scalable output (1-to-50 watts), direct coupling, no feedback, balanced input, simpler circuitry, and no critical adjustments requiring test equipment.
AUDIO ELECTRONICS 2/1997 [Apr 1997] (v.28#2) pg. 8

A 50W ABAB (automatic bias, Class AB) amplifier. Delivers 50W into 8-ohms and 90W into 4-ohms. Also functions as low-distortion Class A operation up to 1W output.
AUDIO ELECTRONICS 2/1997 [Apr 1997] (v.28#2) pg. 12

Designing current-control power amplifiers. Part 1.
AUDIO ELECTRONICS 3/1997 [Jun 1997] (v.28#3) pg. 14
Correction AUDIO ELECTRONICS 4/1997 [Aug 1997] (v.28#4) pg. 36
Added Info AUDIO ELECTRONICS 1/1998 [Jan 1998] (v.29#1) pg. 39

Class-A power modules. Large heat sink is equipped with a complete Class-A power module and SERVO-50 driver board. The output stage can be modified to operate either with or without global feedback.
AUDIO ELECTRONICS 4/1997 [Aug 1997] (v.28#4) pg. 8

Designing current-control power amplifiers. Part 2.
AUDIO ELECTRONICS 4/1997 [Aug 1997] (v.28#4) pg. 26
Added Info AUDIO ELECTRONICS 2/1998 [Apr 1998] (v.29#2) pg. 36

Designing current-control power amplifiers. Part 3.
AUDIO ELECTRONICS 5/1997 [Oct 1997] (v.28#5) pg. 26

Negative feedback in audio amplifiers. What feedback is and some of the advantages, disadvantages and misconceptions surrounding its application in audio.
AUDIO ELECTRONICS 6/1997 [Dec 1997] (v.28#6) pg. 22

New approach to line amps and DACs. Design and construction of a combined line amp and crossover combination which features two dual buffers (one set for subwoofer output and the other for tape output). Also suitable for use as the analog part of an outboard DAC (digital-to-analog converter).
AUDIO ELECTRONICS 4/1998 [Aug 1998] (v.29#4) pg. 8

Zen cousins. Design for a two-gain-stage SE amplifier that borrows heavily from the Zen amplifier designs of Nelson Pass.
AUDIO ELECTRONICS 4/1998 [Aug 1998] (v.29#4) pg. 30
Correction AUDIO ELECTRONICS 2/1999 [Mar 1999] (v.30#2) pg. 49
Added Info AUDIO ELECTRONICS 5/1999 [Sep 1999] (v.30#5) pg. 49

Distortion in audio power amps. An extensive analysis of the factors that contribute to distortion and a design methodology to achieve a low-distortion power amp. Part 1.
AUDIO ELECTRONICS 2/1999 [Mar 1999] (v.30#2) pg. 14

Arjol professional power amplifier. Details of the topology and components selection for an 8-ohm 160-watt unit.
AUDIO ELECTRONICS 3/1999 [Jun 1999] (v.30#3) pg. 18
Added Info AUDIO ELECTRONICS 6/1999 [Nov 1999] (v.30#6) pg. 48

Distortion in audio power amps. Part 2. Distortion in the voltage amplifier and the output stage.
AUDIO ELECTRONICS 3/1999 [Jun 1999] (v.30#3) pg. 30

Distortion in audio power amps. Part 3. How to deal with the various types of distortion.
AUDIO ELECTRONICS 4/1999 [Aug 1999] (v.30#4) pg. 26
Added Info AUDIO ELECTRONICS 1/2000 [Jan 2000] (v.31#1) pg. 49
Added Info AUDIO ELECTRONICS 3/2000 [May 2000] (v.31#3) pg. 49
Added Info AUDIO ELECTRONICS 4/2000 [Jul 2000] (v.31#4) pg. 48

Report on NVA AP50 integrated amplifier kit includes assembly tips and modifications.
AUDIO ELECTRONICS 4/1999 [Aug 1999] (v.30#4) pg. 38

The A40M. A case study in audio amplifier design. Project details for a Class A 40W/channel MOSFET. Includes a discussion of power supplies, hints, and PC-board patterns. Part 1.
AUDIO ELECTRONICS 5/1999 [Sep 1999] (v.30#5) pg. 10
Added Info AUDIO ELECTRONICS 4/2000 [Jul 2000] (v.31#4) pg. 49

Review of the Velleman K4020 MOSFET power amplifier kit includes construction tips and modifications.
AUDIO ELECTRONICS 5/1999 [Sep 1999] (v.30#5) pg. 38
Correction AUDIO ELECTRONICS 1/2000 [Jan 2000] (v.31#1) pg. 49

The A40M. A case study in audio amplifier design. Part 2. Input stage design.
AUDIO ELECTRONICS 6/1999 [Nov 1999] (v.30#6) pg. 22
Added Info AUDIO ELECTRONICS 2/2000 [Mar 2000] (v.31#2) pg. 49

The A40M. A case study in audio amplifier design. Part 3. Input stage design (continued).
AUDIO ELECTRONICS 1/2000 [Jan 2000] (v.31#1) pg. 20

A hybrid tube/MOSFET SE amp. This Class A, single-ended power amplifier combines the warm sound of tubes with the modern power-MOSFET devices.
AUDIO ELECTRONICS 2/2000 [Mar 2000] (v.31#2) pg. 10
Correction AUDIO ELECTRONICS 3/2000 [May 2000] (v.31#3) pg. 49

The A40M. A case study in audio amplifier design. Part 4. Output stage.
AUDIO ELECTRONICS 2/2000 [Mar 2000] (v.31#2) pg. 20

The Power Follower 99. Class A MOSFET amplifier circuit features only one discrete component.
AUDIO ELECTRONICS 3/2000 [May 2000] (v.31#3) pg. 24

The A40M. A case study in audio amplifier design. Part 5. Power supply.
AUDIO ELECTRONICS 3/2000 [May 2000] (v.31#3) pg. 28
Added Info AUDIO ELECTRONICS 5/2000 [Sep 2000] (v.31#5) pg. 42
Added Info AUDIO ELECTRONICS 6/2000 [Nov 2000] (v.31#6) pg. 38

The A40M. A case study in audio amplifier design. Part 6. Construction and layout considerations.
AUDIO ELECTRONICS 4/2000 [Jul 2000] (v.31#4) pg. 30

Upgrading Monarchy's converters and amplifiers. Worthwhile, user-installable upgrades to Monarchy Audio's Models 22C, 33, and 18B D/A converters and the SE-100 Delux and SM-70 power amplifiers.
AUDIO ELECTRONICS 5/2000 [Sep 2000] (v.31#5) pg. 8
Added Info AUDIOXPRESS Jan 2001 (v.32#1) pg. 94

A 30W push-pull 3CX300A1 monoblock. This monaural amplifier features a voltage-driver circuit, using a differential amplifier and a cathode follower to drive a pair of 3CX300A1 vacuum tubes with low impedance.
AUDIOXPRESS Jan 2001 (v.32#1) pg. 10
Added Info AUDIOXPRESS Jun 2001 (v.32#6) pg. 79

Designing your own amplifier. Part 6a. Special output circuits (triode connection, cathode-follower, pentode connection, ultralinear).
AUDIOXPRESS Jan 2001 (v.32#1) pg. 86

A modular hybrid amp system. An Italian design that combines good driving performance with the pleasing sound of tubes.
AUDIOXPRESS Feb 2001 (v.32#2) pg. 8
Added Info AUDIOXPRESS Sep 2001 (v.32#9) pg. 78

Designing your own amplifier. Part 6b. Special output circuits (cathode-coupled ultralinear & Circlotron).
AUDIOXPRESS Feb 2001 (v.32#2) pg. 70

The cure for the common Dynaco MkIII. Build a new two-tube, all-triode driver circuit. Est. cost: $20.
AUDIOXPRESS Mar 2001 (v.32#3) pg. 18

Digital Class-D subwoofer amplifier. Part 1. (1) Pros and cons of true digital amplifiers. (2) Introduction to the SA1 digital amp kit.
AUDIOXPRESS Mar 2001 (v.32#3) pg. 26

High-quality control unit will improve the performance of a modified solid-state Integrated Power Amplifier or a passive control unit. Est. cost: $180.
AUDIOXPRESS Mar 2001 (v.32#3) pg. 36

A 50-watt per channel composite amplifier consists of operational amplifiers cascaded together with a negative-feedback loop around the entire network.
AUDIOXPRESS Apr 2001 (v.32#4) pg. 6
Added Info AUDIOXPRESS Aug 2001 (v.32#8) pg. 80

Digital Class-D subwoofer amplifier. Part 2. Theory behind the SA1 design.
AUDIOXPRESS Apr 2001 (v.32#4) pg. 44

A hybrid tube/MOSFET SE amp. Class A, single-ended power amplifier combines the best of vacuum tubes and power-MOSFET devices.
AUDIOXPRESS May 2001 (v.32#5) pg. 18
Correction AUDIOXPRESS Oct 2001 (v.32#10) pg. 80
Added Info AUDIOXPRESS Jul 2002 (v.33#7) pg. 72

A 211 SE triode amp. Good project for first-time builders of single-ended directly heated triode amplifiers.
AUDIOXPRESS May 2001 (v.32#5) pg. 32

King-size quarter horse power stereo amplifier. Reprint of a 1966 article details the construction of high-power tube amplifier and power supply with a combined weight of over 80 pounds.
AUDIOXPRESS Jun 2001 (v.32#6) pg. 8

A different kind of line amplifier. Design approach leading to a circuit able to drive both terminated 600-ohm transmission lines or a length of high-capacitance audio cable.
AUDIOXPRESS Jun 2001 (v.32#6) pg. 34

An easy solid state preamplifier. Uses Danish-made DACT module amplifiers and peripheral components.
AUDIOXPRESS Jul 2001 (v.32#7) pg. 8
Added Info AUDIOXPRESS Jan 2002 (v.33#1) pg. 72

Odds and evens. An 807 tube-stye power amplifier design uses an even number of audio stages to improve amplifier linearity.
AUDIOXPRESS Jul 2001 (v.32#7) pg. 56
Correction AUDIOXPRESS Jan 2002 (v.33#1) pg. 74

A high-quality two-channel chip amp. This IC-based rear-channel amplifier has several uses to improve the quality of your sound system. Est. cost: $180.
AUDIOXPRESS Aug 2001 (v.32#8) pg. 12
Correction AUDIOXPRESS Oct 2001 (v.32#10) pg. 80

Recreating a 1948 console amp. Capture the classic sound of the Westinghouse AM/FM-Phonograph console, Model H-169 with this basic push-pull amplifier circuit.
AUDIOXPRESS Aug 2001 (v.32#8) pg. 54

Pilot 264. A seemingly generic-looking basic stereo power amp circuit (circa 1962) features a grounded 4-ohm tap and ungrounded "common" and 16-ohm taps.
AUDIOXPRESS Aug 2001 (v.32#8) pg. 87
Added Info AUDIOXPRESS Jan 2002 (v.33#1) pg. 74
Added Info AUDIOXPRESS Feb 2002 (v.33#2) pg. 69
Added Info AUDIOXPRESS Jul 2002 (v.33#7) pg. 72

Choosing coupling capacitor values for audio amplifiers.
AUDIOXPRESS Aug 2001 (v.32#8) pg. 92

A single-ended 6550 amplifier.
AUDIOXPRESS Sep 2001 (v.32#9) pg. 20

Electro-Voice model A-15 push-pull cathode-follower amplifier schematic (circa 1956).
AUDIOXPRESS Sep 2001 (v.32#9) pg. 93
Added Info AUDIOXPRESS Jun 2002 (v.33#6) pg. 66 (Variable damping factor amplifier)

Single-ended push pull amplifier circuit (circa 1962) uses a Sylvania type 7754/7695 tube.
AUDIOXPRESS Sep 2001 (v.32#9) pg. 96
Added Info AUDIOXPRESS Dec 2001 (v.32#12) pg. 73

The trouble with screen grids. How to achieve the results you want with beam power tubes in a monoblock 100W cascode power amplifier.
AUDIOXPRESS Oct 2001 (v.32#10) pg. 24
Added Info AUDIOXPRESS Mar 2002 (v.33#3) pg. 59

Schematic of the Bell Sound 2145 amplifier (circa 1952) which featured an interstage transformer feeding cathode-follower 6SN7s and push-pull 6B4Gs.
AUDIOXPRESS Oct 2001 (v.32#10) pg. 96
Added Info AUDIOXPRESS Apr 2002 (v.33#4) pg. 66

A great first amplifier project. Simple push-pull amplifier circuit has only about 25 parts in each channel and uses inexpensive vacuum tubes.
AUDIOXPRESS Dec 2001 (v.32#12) pg. 18
Added Info AUDIOXPRESS Apr 2002 (v.33#4) pg. 65
Added Info AUDIOXPRESS Aug 2002 (v.33#8) pg. 59
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 62

The revenge KR842VHD amplifier. High-performance single-ended amplifier incorporates a latest-generation tube from Czechoslovakia.
AUDIOXPRESS Dec 2001 (v.32#12) pg. 44

A beginner's push-pull or single-ended amp. This versatile amplifier design lets you sample both PP and SE sound by replacing a few components.
AUDIOXPRESS Jan 2002 (v.33#1) pg. 24
Added Info AUDIOXPRESS Jun 2002 (v.33#6) pg. 68 (Two power supply circuits)
Added Info AUDIOXPRESS Sep 2002 (v.33#9) pg. 63

A PL504 PP amplifier. A Class-A triode push-pull amplifier with little or no feedback and 10W output. Est. cost: $300.
AUDIOXPRESS Jan 2002 (v.33#1) pg. 42
Added Info AUDIOXPRESS Sep 2002 (v.33#9) pg. 64

Pilot AA-410. This classic amplifier (circa 1955) features push-pull circuitry, common tubes, easy-to-get transformers, no adjustments, plenty of power, and a simple chassis layout. A "perfect" starter project.
AUDIOXPRESS Feb 2002 (v.33#2) pg. 72

Zen variations. Part 1: Zen-lightenment. This first in a series on Zen amplifier design will shed some light on simple amp performance. A look at one of the many ways to build a single-stage audio amplifier. This version uses ordinary incancescent light bulb as a constant-current source.
AUDIOXPRESS Mar 2002 (v.33#3) pg. 8

Load-invariant power amplifiers. Understanding amplifier distortion with heavy loading. Part 1.
AUDIOXPRESS Mar 2002 (v.33#3) pg. 28

Self-balancing phase inverter circuit has better high-end performance characteristics than a split-load inverter when used to drive the push-pull output stage of a stereo power amplifier.
AUDIOXPRESS Mar 2002 (v.33#3) pg. 66
Added Info AUDIOXPRESS Nov 2002 (v.33#11) pg. 65

A new Class-B amplifier. Triode amplifier built on an Audio Research D-160 chassis.
AUDIOXPRESS Apr 2002 (v.33#4) pg. 6
Correction AUDIOXPRESS Jun 2002 (v.33#6) pg. 65
Added Info AUDIOXPRESS Nov 2002 (v.33#11) pg. 66

Load-invariant power amplifiers. Understanding amplifier distortion with heavy loading. Part 2.
AUDIOXPRESS Apr 2002 (v.33#4) pg. 40
Added Info AUDIOXPRESS Jan 2003 (v.34#1) pg. 61
Added Info AUDIOXPRESS Aug 2003 (v.34#8) pg. 65

The all-FET line amp (EB-1198/116).
AUDIOXPRESS May 2002 (v.33#5) pg. 28

A practical Circlotron you can build. A high-powered, but seldom-used, amplifier design.
AUDIOXPRESS May 2002 (v.33#5) pg. 34
Added Info AUDIOXPRESS Jan 2003 (v.34#1) pg. 65

A sensible McIntosh 225 refurbish. Involves minimal intrusion, a 6L6/5881 swap for 7591s, and a soft-on, soft-off outboard heater power supply.
AUDIOXPRESS May 2002 (v.33#5) pg. 52
Added Info AUDIOXPRESS Oct 2002 (v.33#10) pg. 62

A five-channel tube home theater amplifier.
AUDIOXPRESS Jun 2002 (v.33#6) pg. 42
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 62

A Marantz 8B replica amplifier. Utilizes the Plitron toroidal transformer and a Svetlana vacuum tube.
AUDIOXPRESS Jul 2002 (v.33#7) pg. 14
Added Info AUDIOXPRESS Mar 2003 (v.34#3) pg. 66

6B4G stereo 90 power amp. Amplifier design offers a solution to the problem of distortion in a push-pull parallel configuration.
AUDIOXPRESS Aug 2002 (v.33#8) pg. 6
Added Info AUDIOXPRESS Feb 2003 (v.34#2) pg. 65

Pilot AA-908. A classic top-of-the-line amplifier circuit (circa 1959).
AUDIOXPRESS Aug 2002 (v.33#8) pg. 67

A 6L6G parallel single-ended stereo amplifier running in triode mode.
AUDIOXPRESS Sep 2002 (v.33#9) pg. 24

Single-stage long-tailed pair phase inverter/driver circuit for use in low-power amplifiers with a dual triode amplifier/phase inverter driving a pair of pentodes or beam power tubes.
AUDIOXPRESS Oct 2002 (v.33#10) pg. 64

Circuit diagram of the Grommes Stereo Precision Amplifier, Model 209 (circa 1950s)
AUDIOXPRESS Oct 2002 (v.33#10) pg. 72
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 67

A 100W-per-channel AB differential input amplifier. An improved version of the Pass/Thagard A75 amplifier. Part 1
AUDIOXPRESS Nov 2002 (v.33#11) pg. 6

Review of the S-5 Electronics K-12M push-pull stereo power amplifier rated for 8W per channel. Available in kit form. Est. cost: $140.
AUDIOXPRESS Nov 2002 (v.33#11) pg. 47
Correction AUDIOXPRESS Jan 2003 (v.34#1) pg. 60 (Measurement charts)
Added Info AUDIOXPRESS Jan 2003 (v.34#1) pg. 67
Added Info AUDIOXPRESS Apr 2003 (v.34#4) pg. 64
Added Info AUDIOXPRESS May 2003 (v.34#5) pg. 64
Added Info AUDIOXPRESS Oct 2003 (v.34#10) pg. 63

A 100W-per-channel AB differential input amplifier. An improved version of the Pass/Thagard A75 amplifier. Part 2. Power supply and construction.
AUDIOXPRESS Dec 2002 (v.33#12) pg. 6

Zen variations. Part 4. The Penultimate Zen. The sum of several incremental improvements to the original Pass Zen amplifier.
AUDIOXPRESS Dec 2002 (v.33#12) pg. 16

High transductance smart power tubes (vacuum tubes). Part 3. Five amplifier projects based on 6C45, 6H30, and 6C46 tubes.
AUDIOXPRESS Jan 2003 (v.34#1) pg. 48

Alternative vacuum tube types for use in power amplifier designs.
AUDIOXPRESS Mar 2003 (v.34#3) pg. 67

A 6AS7/6080-based vacuum tube amplifier design featuring a circlotron configuration.
AUDIOXPRESS Apr 2003 (v.34#4) pg. 32
Added Info AUDIOXPRESS Oct 2003 (v.34#10) pg. 64

The SPP amplifier. This series push-pull amp is easy to build and requires no esoteric tubes or parts.
AUDIOXPRESS May 2003 (v.34#5) pg. 4

A MOSFET update of the Forte 1a amplifier. This modification is based on a simplified version of the Pass/Thagard A75 amplifier. Part 1.
AUDIOXPRESS May 2003 (v.34#5) pg. 10

Advice on the use of individual (versus common-cathode) bias resistors in self-biased power amplifiers employing multiple output tubes.
AUDIOXPRESS May 2003 (v.34#5) pg. 59

60W triode / 100W ultralinear self-contained mono-amplifier with 5 inputs. Est. cost: $350.
AUDIOXPRESS Jun 2003 (v.34#6) pg. 16

A MOSFET update of the Forte 1a amplifier. Part 2.
AUDIOXPRESS Jun 2003 (v.34#6) pg. 60

Hybrid solid-state power amplifiers. (1) Current-boosted op amp. (2) Current- and voltage-boosted op amp. (3) Boosted cascoded op amp. (4) Driven supply op amp.
AUDIOXPRESS Jul 2003 (v.34#7) pg. 6

The DC Revenge E182CC amplifier. A direct-coupled single-ended triode amplifier using readily available indirectly heated vacuum tubes, a simple power supply, and local end tube feedback. Est. cost: $150.
AUDIOXPRESS Jul 2003 (v.34#7) pg. 20

A toroidal line-transformer-driven SV300B single-ended amplifier, featuring a wide power bandwidth at 1W and even 10W output. Latest amp from a noted Japanese designer.
AUDIOXPRESS Jul 2003 (v.34#7) pg. 32

Amplification without distortion. A re-creation of a 1920s style audio amplifier.
AUDIOXPRESS Jul 2003 (v.34#7) pg. 54

Matt's big Class A amplifier. The design and construction of a 20W per channel single-ended Class A audio amplifier with a bipolar input and MOSFET output. It uses a three-stage topology with local and global negative feedback.
AUDIOXPRESS Sep 2003 (v.34#9) pg. 6

A split-load phase inverter consisting of two triode stages (a voltage amplifier followed by the phase inverter).
AUDIOXPRESS Sep 2003 (v.34#9) pg. 56

Zen variations. Part 5. The complementary zen. Exploring single gain-stage amps using a push-pull design.
AUDIOXPRESS Oct 2003 (v.34#10) pg. 6

Experimenting with VMOS power transistors. Circuits include an audio amplifier, analog gate (switch) and high-current variable resistor.
COMPUTERS & ELECTRONICS Mar 1983 (v.21#3) pg. 111

An analysis of the dc (no-signal) condition of a transistor audio amplifier.
CQ. THE RADIO AMATEUR'S JOURNAL Jan 1979 (v.35#1) pg. 72

Circuit for an ultra simple audio amplifier uses the LM380 audio power amplifier chip.
CQ. THE RADIO AMATEUR'S JOURNAL Sep 1979 (v.35#9) pg. 72

General-purpose audio amplifier circuits utilize National Semiconductor ICs. (1) One-half watt audio amplifier using the LM4861. (2) One-watt audio amplifier using the LM4860.
CQ. THE RADIO AMATEUR'S JOURNAL Aug 1995 (v.51#8) pg. 64

A catalog of practical circuits. Part 1. (1) Audio amplifier. (2) Microphone Z matcher.
CQ. THE RADIO AMATEUR'S JOURNAL Nov 1997 (v.53#11) pg. 56

A catalog of practical circuits. Part 2. (1) IC audio amplifiers for operating a speaker. (2) Small-signal RF amplifiers suitable for use in receivers and transmitters and as preamplifiers.
CQ. THE RADIO AMATEUR'S JOURNAL Dec 1997 (v.53#12) pg. 52

Simple 1 watt audio amplifier circuit incorporating the SSM2211 amplifier integrated circuit.
CQ. THE RADIO AMATEUR'S JOURNAL Dec 1998 (v.54#12) pg. 40

Micro-sized amplifier built using surface-mount technology. Est. cost: $20. Use the amp for both a (1) Big-Ear parabolic-reflector microphone and a (2) super-snooper which is built into a headphone-style radio headset.
ELECTRONICS EXPERIMENTERS HANDBOOK 1990 pg. 103, 129

High-power hi-fi audio amplifier for your home or car. Delivers 100-watts RMS of audio into 4-ohms from a single National Semiconductor LM12 power op-amp IC. Separate power supplies (12-volt DC and 110-volt AC) are included. Est. cost: $149 (kit) plus power supply ($99-$119).
ELECTRONICS EXPERIMENTERS HANDBOOK 1990 pg. 147, 127, 128, 129

High-power FET audio stereo amplifier. Uses power MOSFET output transistors in a complementary configuration to provide 250 watts/channel into a 4- or 8-ohm load.
ELECTRONICS EXPERIMENTERS HANDBOOK 1991 pg. 127

Super-simple breadboard vacuum-tube audio amplifier lets you sample the appeal of higher-cost vacuum-tube audio equipment.
ELECTRONICS HOBBYISTS HANDBOOK Fall 1995 pg. 49

Two-watt stereo (or mono) amplifier. Est cost: $10-$15.
ELECTRONICS ILLUSTRATED Jan 1963 (v.6#1) pg. 82

Two-watt mini amplifier for small portables.
ELECTRONICS ILLUSTRATED Jul 1963 (v.6#4) pg. 86

A 120-watt transistorized stereo amplifier.
ELECTRONICS ILLUSTRATED Jan 1964 (v.7#1) pg. 54

Switchbox makes two mono amps into a stereo system.
ELECTRONICS ILLUSTRATED Mar 1964 (v.7#2) pg. 96

A 6-tube, 20-watt integrated stereo amplifier.
ELECTRONICS ILLUSTRATED Jul 1964 (v.7#4) pg. 42

"Big Boom Box". A passive low-pass filter boosts frequencies below 200 cycles in a stereo system, thus increasing the bass volume level.
ELECTRONICS ILLUSTRATED May 1966 (v.9#3) pg. 100

How to service stereo amplifiers. Part 1.
ELECTRONICS ILLUSTRATED May 1971 (v.14#3) pg. 46

How to service stereo amplifiers. Part 2. Preamps and transistor substitution.
ELECTRONICS ILLUSTRATED Jul 1971 (v.14#4) pg. 82

One-tube phono amplifier operates from crystal or ceramic phono cartridge and outputs 1 watt.
ELECTRONICS ILLUSTRATED Sep 1972 (v.15#5) pg. 31

Minimum audio amplifier circuit built around an LM386 IC produces 20-dB gain.
ELECTRONICS NOW Aug 1992 (v.63#8) pg. 14
Added Info ELECTRONICS NOW Nov 1992 (v.63#11) pg. 17
Added Info ELECTRONICS NOW Dec 1992 (v.63#12) pg. 14

Composite audio power amplifiers. Mate a power amplifier IC with a precision op-amp to form a 33-, 40-, or 70-watt amp.
ELECTRONICS NOW Nov 1992 (v.63#11) pg. 38

Determining if your audio system has adequate amplifier power to reproduce the 90-dB dynamic range inherent in CD technology.
ELECTRONICS NOW Jan 1994 (v.65#1) pg. 87

Audio amplifiers. Learn about audio amplifiers in stereos, tuners, and tape and CD players. Includes circuits for simple preamps, RIAA preamps, universal preamp, volume control, tone control, and audio mixer.
ELECTRONICS NOW Mar 1994 (v.65#3) pg. 75
Added Info ELECTRONICS NOW Jul 1994 (v.65#7) pg. 18

Operating principles and circuitry of low-frequency audio power amplifiers based on the bipolar junction transistor. Covers Class AB fundamentals, Class AB variations, amplified diodes, bootstrapping, alternative drivers, and an IC power amplifier.
ELECTRONICS NOW Apr 1994 (v.65#4) pg. 65

High-power hi-fi stereo audio amplifier. One version for home and another is portable for sound reinforcement in halls, auditoriums and theaters. Power output is over 300 watts into 8 ohms. Est. cost: $500. Part 1.
ELECTRONICS NOW Oct 1995 (v.66#10) pg. 33

High-power hi-fi stereo audio amplifier. Part 2.
ELECTRONICS NOW Nov 1995 (v.66#11) pg. 31

Phono Adapter. Simple circuit will let you connect a standard audio source (CD, DVD, cassette deck, ...) to the phono input on a stereo receiver or amplifier.
ELECTRONICS NOW Sep 1999 (v.70#9) pg. 85

Audio gets easier. Using the new LM4862 audio amplifier chip. Several amplifier and oscillator circuits shown.
ELECTRONICS NOW Nov 1999 (v.70#11) pg. 39

Designing silicon-transistor hi-fi amplififers. Part 1. Performance objectives.
ELECTRONICS WORLD Sep 1966 (v.76#3) pg. 23

Designing silicon-transistor hi-fi amplififers. Part 2. Circuit configurations.
ELECTRONICS WORLD Oct 1966 (v.76#4) pg. 34

Designing silicon-transistor hi-fi amplififers. Part 3. Performance of practical circuits.
ELECTRONICS WORLD Nov 1966 (v.76#5) pg. 47

Integrated circuit which delivers 250 mW to an 8-ohm speaker can be used as a headphone driver, low-power audio amplifier, and telephone pickup amplifier.
ELECTRONICS WORLD Feb 1968 (v.79#2) pg. 74

High-gain audio input stage circuit uses a field-effect transistor (FET).
ELECTRONICS WORLD Jul 1969 (v.82#1) pg. 77

A four-channel amplifier for multi-speaker systems.
ELECTRONICS WORLD Nov 1970 (v.84#5) pg. 28

A 2"x4" hi-fi stereo amplifier delivers 3.7 watts per channel into 8 ohms without heat sinks or overheated power transistors. Frequency response is 15-30,000 Hz.
ELECTRONICS WORLD Jan 1971 (v.85#1) pg. 34

Convert a pocket-size transistor radio to a tuner for another amplifier or a low-power amplifier for phono, tape recorder, etc.
ELEMENTARY ELECTRONICS Sep-Oct 1969 (v.9#1) pg. 62

A complete amplifier, requiring only 9 volts, is small enough to cement on the back of the magnet of a small speaker. Response will be flat from 100 to 20,000 KHz. Uses an integrated circuit power amplifier. Can be used in an intercom.
ELEMENTARY ELECTRONICS Nov-Dec 1970 (v.10#5) pg. 41

Experimenting with the latest low-power digital amplifiers. Build an amplifier and add a loudspeaker to boost the output of portable transistor radios or to use as a portable electronic microphone.
ELEMENTARY ELECTRONICS Mar-Apr 1975 (v.15#2) pg. 59

Computer program written in TRS-80 Level 2 BASIC is used to help design audio circuits. It is handy when plotting amplifier input sensitivity and output power chart or curves, or when designing or calculating filters, the effects of capacitance versus resistance, plotting frequency cut-offs, ... etc.
ELEMENTARY ELECTRONICS Nov-Dec 1979 (v.19#6) pg. 52

A self-bias servo for push-pull output tube amplifiers. This unit eliminates the need to adjust DC bias on output vacuum tubes, does not affect the audio operation of the amplifier (a Dyna Mark III) , and is inexpensive and reliable. Est. cost: $15.
GLASS AUDIO 0/1988 (v.1) pg. 9
Added Info GLASS AUDIO 2/1989 (v.1#2) pg. 34, 35, 37, 38
Added Info GLASS AUDIO 1/1990 (v.2#1) pg. 39
Added Info GLASS AUDIO 2/1990 (v.2#2) pg. 40
Added Info GLASS AUDIO 1/1991 (v.3#1) pg. 52
Added Info GLASS AUDIO 3/1992 (v.4#3) pg. 45
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 39
Added Info GLASS AUDIO 2/1994 (v.6#2) pg. 22

A vacuum tube power stereo amplifier with solid-state regulation. Modifying the Dynaco ST-70 by replacing the driver stage with an all triode (vacuum tube) design contained on two circuit boards.
GLASS AUDIO 1/1989 (v.1#1) pg. 1
Correction GLASS AUDIO 2/1989 (v.1#2) pg. 34
Added Info GLASS AUDIO 1/1991 (v.3#1) pg. 50
Added Info GLASS AUDIO 2/1991 (v.3#2) pg. 52, 54
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 34

Amplifier design Q & A. Use of loop feedback and importance of AC load line as applied to a high-level stage built around a 12AX7 vacuum tube.
GLASS AUDIO 1/1989 (v.1#1) pg. 24

Rejuvenating the Dynaco Mark IV tube-type audio amplifier. Includes an improved bias circuit, power supply, DC filament supply and alternatives to the 7199 tube.
GLASS AUDIO 2/1989 (v.1#2) pg. 8
Added Info GLASS AUDIO 2/1990 (v.2#2) pg. 42

Comparison test of five modification kits for the Dynaco ST-70 vacuum tube style audio amplifier.
GLASS AUDIO 2/1989 (v.1#2) pg. 26
Added Info GLASS AUDIO 1/1990 (v.2#1) pg. 36
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 34

Build 70 watts of McIntosh tube power. Tube-type audio amplifier incorporates an output transformer salvaged from the McIntosh MA230 hybrid integrated amplifier. Includes circuit for power supplies, voltage doubler, time delays, amplifier circuit, etc. Est. cost: $400-$600 per pair.
GLASS AUDIO 1/1990 (v.2#1) pg. 1
Added Info GLASS AUDIO 2/1990 (v.2#2) pg. 43, 46
Added Info GLASS AUDIO 1/1991 (v.3#1) pg. 48, 53, 54
Correction GLASS AUDIO 3/1992 (v.4#3) pg. 46

Understanding tube phase inverters as found in a vacuum tube power amplifier.
GLASS AUDIO 1/1990 (v.2#1) pg. 12
Added Info GLASS AUDIO 2/1990 (v.2#2) pg. 46
Added Info GLASS AUDIO 1/1991 (v.3#1) pg. 45
Correction GLASS AUDIO 2/1991 (v.3#2) pg. 51, 58
Added Info GLASS AUDIO 1/1992 (v.4#1) pg. 46
Added Info GLASS AUDIO 1/1995 (v.7#1) pg. 16, 45
Added Info GLASS AUDIO 2/1995 (v.7#2) pg. 57

A transformerless output tube-type audio amplifier will output 35W into 16 ohms. Built using standard, good quality parts. Est. cost: $500.
GLASS AUDIO 2/1990 (v.2#2) pg. 1
Added Info GLASS AUDIO 1/1991 (v.3#1) pg. 53, 54
Added Info GLASS AUDIO 1/1992 (v.4#1) pg. 48
Added Info GLASS AUDIO 3/1994 (v.6#3) pg. 39
Added Info GLASS AUDIO 6/1996 (v.8#6) pg. 56

Unveiling the Silver Seven. Schematic and parts list for constructing a 500-watt monoblock audio amplifier incorporating 14 parallel 6550 vacuum tubes.
GLASS AUDIO 2/1990 (v.2#2) pg. 30
Added Info GLASS AUDIO 2/1992 (v.4#2) pg. 53

Schematic for the Radford STA 15 basic amplifier circuit and power supply (circa 1965).
GLASS AUDIO 2/1990 (v.2#2) pg. 39
Added Info GLASS AUDIO 4/1994 (v.6#4) pg. 28

Rebuilding tube amplifiers. Restoration project on an H.H. Scott LK-72 integrated amp (circa 1960s) serves to illustrate the process.
GLASS AUDIO 1/1991 (v.3#1) pg. 1
Added Info GLASS AUDIO 2/1991 (v.3#2) pg. 58, 60
Added Info GLASS AUDIO 1/1992 (v.4#1) pg. 43, 46
Added Info GLASS AUDIO 2/1992 (v.4#2) pg. 56
Added Info GLASS AUDIO 4/1992 (v.4#4) pg. 36
Added Info GLASS AUDIO 4/1994 (v.6#4) pg. 47

Classical glass. Schematic of the Eico Model HF20 high-fidelity amplifier.
GLASS AUDIO 1/1991 (v.3#1) pg. 38

The 6BX7 amplifier. An all-triode, 10W VT amplifier with active voltage regulation.
GLASS AUDIO 2/1991 (v.3#2) pg. 9
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 38

Modifying the Dynaco ST-70 with triode mode input stage. By simply changing capacitor connections, the 7199 pentode input stage functions as a triode whose lower plate resistance results in greater bandwidth and improved sound quality.
GLASS AUDIO 1/1992 (v.4#1) pg. 18
Correction GLASS AUDIO 2/1992 (v.4#2) pg. 54
Added Info GLASS AUDIO 2/1992 (v.4#2) pg. 54
Added Info GLASS AUDIO 3/1992 (v.4#3) pg. 44
Added Info GLASS AUDIO 4/1992 (v.4#4) pg. 39
Added Info GLASS AUDIO 2/1993 (v.5#2) pg. 38, 42
Added Info GLASS AUDIO 3/1993 (v.5#3) pg. 41

A 20/20 dual monoblock tube amplifier incorporates the RCA design push-pull Class AB1, 7868 beam power amplifier.
GLASS AUDIO 1/1992 (v.4#1) pg. 33
Added Info GLASS AUDIO 2/1992 (v.4#2) pg. 56
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 41
Added Info GLASS AUDIO 2/1993 (v.5#2) pg. 42

Vacuum-tube AC feedback amplifiers. An explanation of the 1+1 and 2+1 cascade amplifier concept.
GLASS AUDIO 2/1992 (v.4#2) pg. 14
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 27
Added Info GLASS AUDIO 1/1994 (v.6#1) pg. 32 (Dual 1+1 cascade amplifier)

A phase inverter for bridge operation of any stereo amp.
GLASS AUDIO 2/1992 (v.4#2) pg. 53

Purist tube amplifier: a timeless classic. Schematic and parts list for a unique, high-quality amplifier built originally in 1957. It features a tube-regulated power supply, differential front end, cross-coupled phase inverter, and the presence of only one capacitor in the signal path.
GLASS AUDIO 3/1992 (v.4#3) pg. 32
Added Info GLASS AUDIO 2/1993 (v.5#2) pg. 41
Added Info GLASS AUDIO 4/1993 (v.5#4) pg. 44
Added Info GLASS AUDIO 3/2000 (v.12#3) pg. 60

What about Bordeaux: The secrets of Jadis JA-80 and JA-200 amplifiers.
GLASS AUDIO 3/1992 (v.4#3) pg. 40
Added Info GLASS AUDIO 1/1993 (v.5#1) pg. 27
Added Info GLASS AUDIO 3/1996 (v.8#3) pg. 69

60W OTL/OCL triode power amplifier. Build an output-transformerless (OTL) vacuum-tube power amplifier.
GLASS AUDIO 4/1992 (v.4#4) pg. 1
Added Info GLASS AUDIO 1/1994 (v.6#1) pg. 47
Added Info GLASS AUDIO 3/1994 (v.6#3) pg. 47

A 40W Class A triode amplifier.
GLASS AUDIO 1/1993 (v.5#1) pg. 1
Added Info GLASS AUDIO 6/1998 (v.10#6) pg. 52 (Tube heaters)

Tubesaurus Rex. Audio amp which incorporates long-forgotten tubes of yesteryear with modern technology for a best-of-both worlds amplifier.
GLASS AUDIO 1/1993 (v.5#1) pg. 18

Vintage glass. Schematic and parts list for the Avantic Beam Echo DL7-35 power amplifier.
GLASS AUDIO 1/1993 (v.5#1) pg. 23

Professional tube line driver. Advice on designing tube equipment for professional audio use that deals with the dual problems of driving low input impedance devices and long cable runs.
GLASS AUDIO 2/1993 (v.5#2) pg. 6
Correction GLASS AUDIO 4/1993 (v.5#4) pg. 41
Added Info GLASS AUDIO 1/1995 (v.7#1) pg. 40
Added Info GLASS AUDIO 3/1995 (v.7#3) pg. 57
Correction GLASS AUDIO 4/1995 (v.7#4) pg. 50
Added Info GLASS AUDIO 6/1995 (v.7#6) pg. 62
Added Info GLASS AUDIO 2/1996 (v.8#2) pg. 62

The mu stage. Optimizing the audio gain stage. Circuits covered include the TTSA (two-tube series amplifier), SRPP (shunt-regulated push-pull), mu stage, hybrid mu stage, differential input mu stage, etc.
GLASS AUDIO 2/1993 (v.5#2) pg. 12
Added Info GLASS AUDIO 3/1993 (v.5#3) pg. 38
Added Info GLASS AUDIO 4/1993 (v.5#4) pg. 40
Added Info GLASS AUDIO 2/1994 (v.6#2) pg. 40
Added Info GLASS AUDIO 4/1994 (v.6#4) pg. 45, 48
Added Info GLASS AUDIO 1/1995 (v.7#1) pg. 38
Added Info GLASS AUDIO 3/1995 (v.7#3) pg. 55, 65
Correction GLASS AUDIO 4/1995 (v.7#4) pg. 48
Added Info GLASS AUDIO 5/1996 (v.8#5) pg. 30

Tip on converting a Dynaco ST-35 stereo amp for mono operation.
GLASS AUDIO 2/1993 (v.5#2) pg. 34

Circuit modifications for the Dynaco MK III tube amplifier. (1) Triode mode input stage. (2) 6550 control grid.
GLASS AUDIO 2/1993 (v.5#2) pg. 38, 41

Feedback RIAA equalization. Formulas applicable to feedback circuits with limited gain amplifiers (of which the tube type is typical).
GLASS AUDIO 3/1993 (v.5#3) pg. 20

Balanced tube alternatives. An examination of the characteristics of push/pull amplifiers and their harmonic distortion, as it relates specifically to the electrical characteristics of the vacuum tubes used.
GLASS AUDIO 4/1993 (v.5#4) pg. 12

Transformer coupled WE-300B (vacuum tube) single-ended stereo amplifier.
GLASS AUDIO 1/1994 (v.6#1) pg. 1
Added Info GLASS AUDIO 1/1996 (v.8#1) pg. 47 (Mu-follower driver)
Added Info GLASS AUDIO 3/1997 (v.9#3) pg. 1 (Improved version)
Added Info GLASS AUDIO 3/1998 (v.10#3) pg. 49
Added Info AUDIOXPRESS Oct 2001 (v.32#10) pg. 90 (Improved version tube harmonics)
Added Info AUDIOXPRESS Aug 2002 (v.33#8) pg. 68 (Modification of 3/1997 improved version)

Preventing blown output transformers in tube amplifiers that are operated without speakers connected.
GLASS AUDIO 1/1994 (v.6#1) pg. 34
Added Info GLASS AUDIO 3/1994 (v.6#3) pg. 50
Added Info GLASS AUDIO 4/1994 (v.6#4) pg. 46
Added Info GLASS AUDIO 1/1995 (v.7#1) pg. 47

Asymmetrical mu-follower circuits use two single triodes, a double triode, or a triode pentode. Gives low distortion, low output impedance, and high gain at the same time. Can be used in preamplifiers or as an electrostatic headphone driver.
GLASS AUDIO 1/1994 (v.6#1) pg. 42

Cascode amplifier construction. A new way to look at a cascode, breaking it into two well-known circuits to better understand its composite behavior.
GLASS AUDIO 2/1994 (v.6#2) pg. 1
Added Info GLASS AUDIO 3/1994 (v.6#3) pg. 46

Advice on using 6A5G triode output tubes in a Gram G60AMS power amplifier.
GLASS AUDIO 2/1994 (v.6#2) pg. 33
Added Info GLASS AUDIO 3/1994 (v.6#3) pg. 49

Troubleshooting a Dynaco Mark VI where the 8417 output tubes glow cherry red while setting the bias.
GLASS AUDIO 2/1994 (v.6#2) pg. 35
Added Info GLASS AUDIO 4/1994 (v.6#4) pg. 28
Added Info GLASS AUDIO 3/1995 (v.7#3) pg. 57

Cathanode follower circuits use a cathode follower to drive an anode follower (an inverter with 100% voltage feedback).
GLASS AUDIO 2/1994 (v.6#2) pg. 38

Modified White follower eliminates the rising subsonic response caused by the blocking capacitor in the feedback divider of the common two tube line amplifier.
GLASS AUDIO 2/1994 (v.6#2) pg. 38

Differential series feedback pair circuit is based on a modification of the White follower. Features completely stable subsonic response from DC coupling between output and feedback input. High-frequency response is also very stable.
GLASS AUDIO 3/1994 (v.6#3) pg. 18
Correction GLASS AUDIO 4/1994 (v.6#4) pg. 51
Added Info GLASS AUDIO 5/1996 (v.8#5) pg. 60

The importance of balance in push-pull amplifiers.
GLASS AUDIO 4/1994 (v.6#4) pg. 16

Kit report on the Maplin Electronics "Millennium 4-20" 20W valve power amplifier.
GLASS AUDIO 4/1994 (v.6#4) pg. 34
Added Info GLASS AUDIO 3/1996 (v.8#3) pg. 69

Switchable circuit for converting a push-pull amplifier to a single-ended type.
GLASS AUDIO 4/1994 (v.6#4) pg. 38

Kit report on the Audio Electronic Supply (AES) SE-1 7-watt single-ended triode (SET) amplifier.
GLASS AUDIO 1/1995 (v.7#1) pg. 34
Added Info GLASS AUDIO 3/1995 (v.7#3) pg. 28 (Modification to add gain stage)
Added Info GLASS AUDIO 5/1995 (v.7#5) pg. 59

DC-coupled cathode follower ideas for experimenters working with vacuum tube amplifiers.
GLASS AUDIO 1/1995 (v.7#1) pg. 46

A 15-watt triode power amplifier. Includes test results of experiments with vacuum tubes of various shapes, sizes, and configurations.
GLASS AUDIO 2/1995 (v.7#2) pg. 14
Added Info GLASS AUDIO 3/1995 (v.7#3) pg. 56
Added Info GLASS AUDIO 3/1997 (v.9#3) pg. 68

Brief look at the advantage/disadvantage of parallel single-ended (PSE) tube design audio amplifiers.
GLASS AUDIO 2/1995 (v.7#2) pg. 42

Tip on replacing the EL34 vacuum tubes in a Dyna ST-70 with Sovtek 5881s.
GLASS AUDIO 2/1995 (v.7#2) pg. 43

Single-ended glory. Single-ended audio amplifier uses the old 45 or UX-245 directly heated triode vacuum tube. Output is only 1 watt. Est. cost: $100.
GLASS AUDIO 3/1995 (v.7#3) pg. 1
Added Info GLASS AUDIO 6/1995 (v.7#6) pg. 70
Added Info GLASS AUDIO 2/1996 (v.8#2) pg. 44
Added Info GLASS AUDIO 6/1996 (v.8#6) pg. 56
Added Info GLASS AUDIO 1/1997 (v.9#1) pg. 44, 52
Added Info GLASS AUDIO 3/1997 (v.9#3) pg. 58

The suitability of the 6DJ8 vacuum tube for audio. Valuable information for designing audio amplification circuits using dual triodes.
GLASS AUDIO 3/1995 (v.7#3) pg. 10
Added Info GLASS AUDIO 6/1995 (v.7#6) pg. 66
Added Info GLASS AUDIO 5/1996 (v.8#5) pg. 58

Novel audio output circuit with the contradictory name "single-ended push-pull".
GLASS AUDIO 3/1995 (v.7#3) pg. 53
Added Info GLASS AUDIO 5/1995 (v.7#5) pg. 62
Added Info GLASS AUDIO 3/1996 (v.8#3) pg. 70

Tips on transforming the output stage of a modified Dyna ST-70 from the conventional ultralinear mode to a triode mode.
GLASS AUDIO 3/1995 (v.7#3) pg. 54
Added Info GLASS AUDIO 5/1995 (v.7#5) pg. 57

Schematic for the Sun Radio CR-10 amplifier (circa 1948).
GLASS AUDIO 3/1995 (v.7#3) pg. 62

Diff amp driver with BJT source. This driver circuit/stereo amplifier performs better than most other, more complex, circuits.
GLASS AUDIO 4/1995 (v.7#4) pg. 16
Correction GLASS AUDIO 2/1996 (v.8#2) pg. 58

Reconstructing old amplifiers. A description of several circuit design techniques found to be most effective in improving a number of different amplifiers. These tips should work well on most older, well-designed tube amps with good-quality transformers. Includes schematics and parts list for (1) Modified Dynaco ST-70 and (2) Heath W-5M.
GLASS AUDIO 6/1995 (v.7#6) pg. 1
Correction GLASS AUDIO 2/1996 (v.8#2) pg. 61
Correction GLASS AUDIO 3/1997 (v.9#3) pg. 54

The amplifier distortion story. Part 1. The causes of distortion in amplifiers and the use of tube transfer characteristics to investigate performance.
GLASS AUDIO 6/1995 (v.7#6) pg. 20

Linear output stages for use with modern loudspeakers. Methods of connecting same-type devices in push-pull configuration amplifiers.
GLASS AUDIO 6/1995 (v.7#6) pg. 34

The 6DQ5 single-ended power amp. A case for using tetrodes in audio circuits because of their higher efficiency and lesser distortion.
GLASS AUDIO 6/1995 (v.7#6) pg. 44

Twin pentode input stage (driver stage). Schematics of the most-used input stages for push-pull amplifiers.
GLASS AUDIO 6/1995 (v.7#6) pg. 73

Driving the 300B. Tune up a 300B-based amplifier with the "ultimate" driver setup.
GLASS AUDIO 1/1996 (v.8#1) pg. 16
Added Info GLASS AUDIO 4/1996 (v.8#4) pg. 66, 67, 69
Correction GLASS AUDIO 5/1996 (v.8#5) pg. 61, 63

Cautionary note on the use of television HOTs (horizontal-sweep output tubes) in high-fidelity audio power amplifier circuits.
GLASS AUDIO 1/1996 (v.8#1) pg. 53

Build a single-ended pentode amplifier. Includes a list of the best-performing vacuum tubes for this configuration.
GLASS AUDIO 2/1996 (v.8#2) pg. 1
Added Info GLASS AUDIO 6/1996 (v.8#6) pg. 68

In search of the perfect vacuum tube. Advice on careful examination of a tube's physical makeup and the use of directly-heated triodes for best results. Includes information and schematics for a directly heated triode amplifier.
GLASS AUDIO 2/1996 (v.8#2) pg. 12
Added Info GLASS AUDIO 6/1996 (v.8#6) pg. 63, 65
Added Info GLASS AUDIO 2/1997 (v.9#2) pg. 60

New life for old tubes. Advice on using old TV and radio vacuum tubes in audio circuits.
GLASS AUDIO 2/1996 (v.8#2) pg. 46
Added Info GLASS AUDIO 5/1996 (v.8#5) pg. 55

Harman-Kardon Citation II stereo amplifier schematic.
GLASS AUDIO 2/1996 (v.8#2) pg. 66

Excerpt from UNDERSTANDING HI-FI CIRCUITS looks at output stages and the merits of triode or pentode operation of the output vacuum tubes.
GLASS AUDIO 3/1996 (v.8#3) pg. 1

Stereo half watter. Both a bare-bones and a deluxe circuit are shown (the deluxe has four extra circuits to improve tube service). An ideal amplifier for background music listening. Est. cost: $100.
GLASS AUDIO 3/1996 (v.8#3) pg. 22

A new single-ended SV811-10 amp. How to reuse an old chassis with a new tube type, the Svetlana SV811-10 audio power triode, which is a low-mu version of the classic 811A transmitting triode.
GLASS AUDIO 3/1996 (v.8#3) pg. 34
Added Info GLASS AUDIO 1/1997 (v.9#1) pg. 46, 51
Added Info GLASS AUDIO 3/1997 (v.9#3) pg. 59, 60
Added Info GLASS AUDIO 5/1997 (v.9#5) pg. 12 (Improvements)
Added Info GLASS AUDIO 3/1998 (v.10#3) pg. 51

Dual single-ended amplifier. Description of a new technique which uses two single-ended amplifiers per channel in such a way that the total power is added while reducing the harmonic distortion.
GLASS AUDIO 3/1996 (v.8#3) pg. 42

Report on the Velleman 100W per channel stereo valve amplifier kit. Includes tips on construction and testing.
GLASS AUDIO 3/1996 (v.8#3) pg. 65

Harmonic cancellation improves the SE (single-ended) amplifier. Unconventional polarity hook-up uses harmonic cancellation to keep THD levels in check.
GLASS AUDIO 4/1996 (v.8#4) pg. 1

Report on the Arion Acoustics Ltd. (N. Ireland) Adonis 20W triode-coupled, line-level integrated amplifier kit. Includes tips on assembly and testing.
GLASS AUDIO 4/1996 (v.8#4) pg. 56
Correction GLASS AUDIO 5/1996 (v.8#5) pg. 62
Added Info GLASS AUDIO 2/1997 (v.9#2) pg. 63

Modify a low-power push-pull amplifier which uses the 6BQ5 vacuum tube to accept the 6CW5 tube which will produce less distortion.
GLASS AUDIO 4/1996 (v.8#4) pg. 64
Added Info GLASS AUDIO 6/1996 (v.8#6) pg. 66

Clarification of the effects of negative feedback upon the output impedance of an amplifier.
GLASS AUDIO 4/1996 (v.8#4) pg. 72

A 15W single-ended power amplifier that uses the Russian 6C33C-B triode vacuum tube.
GLASS AUDIO 5/1996 (v.8#5) pg. 1
Correction GLASS AUDIO 2/1997 (v.9#2) pg. 56

Improved vacuum tube amplifier circuit models for SPICE simulations.
GLASS AUDIO 5/1996 (v.8#5) pg. 18
Correction GLASS AUDIO 6/1996 (v.8#6) pg. 62

Enhanced-mode operation of pentodes in a 16W single-ended amplifier design which utilizes TV-sweep vacuum tubes.
GLASS AUDIO 5/1996 (v.8#5) pg. 50
Correction GLASS AUDIO 6/1996 (v.8#6) pg. 66

Information on modifying a Dynaco ST-70 to use the 6B4G or 6AV5 vacuum tube.
GLASS AUDIO 5/1996 (v.8#5) pg. 54
Added Info GLASS AUDIO 1/1997 (v.9#1) pg. 49

Kismet. A simple 2A3-based single-ended amplifier.
GLASS AUDIO 6/1996 (v.8#6) pg. 1
Added Info GLASS AUDIO 2/1997 (v.9#2) pg. 65

Advice on selecting substitute vacuum tubes when building an audio amplifier on the remains of an EICO ST-70.
GLASS AUDIO 6/1996 (v.8#6) pg. 59

A triode-loaded pentode input stage for single-end amplifiers.
GLASS AUDIO 6/1996 (v.8#6) pg. 60

Schematic and brief history of the 50W PERI power amplifier (circa 1957).
GLASS AUDIO 6/1996 (v.8#6) pg. 72

Schematic and parts list for the EICO HF60 60W audio amplifier.
GLASS AUDIO 6/1996 (v.8#6) pg. 74

4-250A beam tetrode power amplifier utilizes a transmitting tube for longer life, greater reliability, and more stable operation.
GLASS AUDIO 1/1997 (v.9#1) pg. 1
Correction GLASS AUDIO 3/1997 (v.9#3) pg. 55
Added Info GLASS AUDIO 4/1997 (v.9#4) pg. 57
Added Info GLASS AUDIO 5/1997 (v.9#5) pg. 57

Differential line amp with tubes. Design uses one ECC83 and two ECC81s to produce two high-level, out-of-phase signals needed to drive push-pull output stages.
GLASS AUDIO 1/1997 (v.9#1) pg. 24

Tip on converting a PP KT88 valve amp from UL configuration to triode-connected.
GLASS AUDIO 1/1997 (v.9#1) pg. 44

Tip on replacement or substitute power tubes for the LUXMAN MB3045 power amplifier which uses the 8045G vacuum tube.
GLASS AUDIO 1/1997 (v.9#1) pg. 45

Modifications to the Quicksilver mono amplifier to replace the 8417 Pinal vacuum tubes with 6550 tubes.
GLASS AUDIO 2/1997 (v.9#2) pg. 62

Simple gain circuits. An excerpt from a new book on designing vacuum tube audio circuits entitled "Beginner's Guide to Audio Tube Design".
GLASS AUDIO 3/1997 (v.9#3) pg. 30
Added Info GLASS AUDIO 5/1998 (v.10#5) pg. 66

A battery tube hi-fi amplifier. A simple battery-powered breadboard-style amplifier uses an single vacuum tube and eliminates the high-voltage danger. Features low distortion, no negative feedback, and a reasonably flat response over the audio spectrum.
GLASS AUDIO 3/1997 (v.9#3) pg. 38
Added Info GLASS AUDIO 5/1997 (v.9#5) pg. 63
Added Info GLASS AUDIO 5/1998 (v.10#5) pg. 67
Added Info AUDIOXPRESS Feb 2003 (v.34#2) pg. 62

Single-ended amplifier output impedance. Part 1. Includes advice on interfacing the amp with loudspeakers.
GLASS AUDIO 3/1997 (v.9#3) pg. 42

Advice on converting a Sound Valves VTA-70 amplifier (an ultralinear 35W with EL34 outputs) to triode.
GLASS AUDIO 3/1997 (v.9#3) pg. 50

Advice on modifying a PPP2A3 amplifier (circa 1937) to use older rectifiers and 76 tubes.
GLASS AUDIO 3/1997 (v.9#3) pg. 52
Correction GLASS AUDIO 5/1997 (v.9#5) pg. 61
Added Info GLASS AUDIO 3/1998 (v.10#3) pg. 54

Vintage glass. Schematic and parts list for the Eico HF20 amplifier.
GLASS AUDIO 3/1997 (v.9#3) pg. 69

Behemoth tamed. Modifying the Dynaco MkVI power amplifier to run on 6CA7/EL34 output tubes in place of the original matched quad of 8417 tubes.
GLASS AUDIO 5/1997 (v.9#5) pg. 36

How to bridge the channels together in a tube-type transformer-coupled amplifier for use as a center-channel amp.
GLASS AUDIO 5/1997 (v.9#5) pg. 50

Advice on using a 100TH transmitting triode in a vacuum tube audio amplifier circuit.
GLASS AUDIO 5/1997 (v.9#5) pg. 50
Correction GLASS AUDIO 4/1998 (v.10#4) pg. 58

Advice on lengthening the life of 7591 vacuum tubes in older audio equipment by (1) decreasing the negative grid bias, (2) lowering plate voltage, and/or (3) improved cooling.
GLASS AUDIO 5/1997 (v.9#5) pg. 52

Vintage glass. Schematic of the classic Pilot AA-901 triode amplifier which features a Williamson design and triode-connected KT66s.
GLASS AUDIO 5/1997 (v.9#5) pg. 69

Single-ended amplifier output impedance. Part 2. Effects at low frequencies.
GLASS AUDIO 6/1997 (v.9#6) pg. 28

The search for linearity (the perfect linear system) examines active load triodes. Part 3. Preamp and power amp circuits.
GLASS AUDIO 6/1997 (v.9#6) pg. 42
Correction GLASS AUDIO 2/1998 (v.10#2) pg. 44
Added Info GLASS AUDIO 4/1998 (v.10#4) pg. 56
Added Info GLASS AUDIO 2/1999 (v.11#2) pg. 60

Product review of the Single-Ended Experimenter's tube amplifier kit from Electronic Tonalities. Includes construction tips and modification ideas.
GLASS AUDIO 6/1997 (v.9#6) pg. 54
Added Info GLASS AUDIO 2/1998 (v.10#2) pg. 47

Low-voltage tube/MOSFET line amp. This EB-797/203 hybrid amplifier uses a 24-volt anode supply and 6.3-volts for heating. Open-loop gain is 53 dB.
GLASS AUDIO 1/1998 (v.10#1) pg. 1

Product review of the Miyabe VP-300BD stereo amplifier kit. Includes construction tips.
GLASS AUDIO 1/1998 (v.10#1) pg. 38
Added Info GLASS AUDIO 2/1998 (v.10#2) pg. 44
Added Info GLASS AUDIO 4/1998 (v.10#4) pg. 59

40W triode and 60W ultralinear amplifier. An update of a 1959 design which features push-pull 6550s preceded by a duo-triode long-tailed phase inverter and a pentode first stage. The amp requires a 1.8V (RMS) drive signal for 40W output in the triode mode, and a 2V (RMS) drive signal for 60W output in the UL mode. Est. cost: $500.
GLASS AUDIO 2/1998 (v.10#2) pg. 1
Added Info GLASS AUDIO 4/1998 (v.10#4) pg. 58
Correction GLASS AUDIO 1/1999 (v.11#1) pg. 52
Added Info GLASS AUDIO 5/1999 (v.11#5) pg. 62
Added Info GLASS AUDIO 2/2000 (v.12#2) pg. 61
Added Info AUDIOXPRESS Mar 2001 (v.32#3) pg. 82

An indirectly heated single-ended R120 triode amplifier.
GLASS AUDIO 3/1998 (v.10#3) pg. 1

Understanding the role of feedback in audio systems to (1) reduce distortion, (2) adjust frequency response, (3) improve stability from variation due to component deviation or fluctuation, (4) adjust or control input and/or output impedance, ... etc.
GLASS AUDIO 3/1998 (v.10#3) pg. 34

Circuit modifications to the Quad I amplifier (circa 1947) to convert it into a Quad II with identical component values.
GLASS AUDIO 3/1998 (v.10#3) pg. 62

Schematics detail an Italian 3W single-ended amplifier (circa 1960s).
GLASS AUDIO 3/1998 (v.10#3) pg. 66
Added Info GLASS AUDIO 1/1999 (v.11#1) pg. 59
Added Info GLASS AUDIO 6/1999 (v.11#6) pg. 58
Correction GLASS AUDIO 2/2000 (v.12#2) pg. 60

Product review of Sonic Frontiers' Assemblage ST-40 power amplifier kit.
GLASS AUDIO 4/1998 (v.10#4) pg. 50

The T275 amplifier (circa 1973). Parts list and schematics for (1) main power amplifiers and (2) power supply and AC distribution.
GLASS AUDIO 4/1998 (v.10#4) pg. 68

Cascode power-amplifier circuits. A hybrid audio amplifier combines cascode pairing of a JFET or a MOSFET with a vacuum tube. The advantages include high input impedance, low drift, low noise, and high gain (60 dB). Part 1. Circuit utilizing the KT88 tube.
GLASS AUDIO 5/1998 (v.10#5) pg. 1
Added Info GLASS AUDIO 2/1999 (v.11#2) pg. 61

Canceling second-harmonic distortion in SE (single-ended) triode amplifiers by adjusting the bias on the voltage amplifier.
GLASS AUDIO 5/1998 (v.10#5) pg. 30

70W low-distortion triode mono-amplifier. Features push-pull, parallel 6550s connected as triodes preceded by a duotriode long-tailed phase inverter and a pentode first stage. Requires a 2.3V (RMS) drive signal for 70W output. Est. cost: $400.
GLASS AUDIO 5/1998 (v.10#5) pg. 38
Correction GLASS AUDIO 1/1999 (v.11#1) pg. 52
Correction GLASS AUDIO 3/1999 (v.11#3) pg. 58
Correction GLASS AUDIO 1/2000 (v.12#1) pg. 58
Added Info AUDIOXPRESS Mar 2001 (v.32#3) pg. 82

Direct coupling the 6KG6/EL509. Experimental amplifier design shows how to achieve 10W of clean SE (single-ended) power in a DC-coupled screen-driven unit.
GLASS AUDIO 5/1998 (v.10#5) pg. 48
Correction GLASS AUDIO 1/1999 (v.11#1) pg. 52

Cascode power-amplifier circuits. Part 2. Circuit utilizing the 6C33C tube.
GLASS AUDIO 6/1998 (v.10#6) pg. 26
Correction GLASS AUDIO 3/1999 (v.11#3) pg. 58

Product review of the Atma-Sphere M-60 Mk.II output-transformerless (OTL) amplifier kit. Includes construction advice and test results.
GLASS AUDIO 6/1998 (v.10#6) pg. 56

Cathode-driven power triodes. A new triode drive topology that circumvents the problems generally associated with power triode schemes.
GLASS AUDIO 1/1999 (v.11#1) pg. 26

I built an amplifier, you can too. Advice from a first-time builder who restored an all-tube, stereo integrated amplifier. Includes tips on salvaging discarded electronic stuff.
GLASS AUDIO 1/1999 (v.11#1) pg. 38
Correction GLASS AUDIO 4/1999 (v.11#4) pg. 56

Hi-fi Mazda amplifier schematic (circa 1935) utilizes a rare PP3/250 or PP5/400 output triode.
GLASS AUDIO 1/1999 (v.11#1) pg. 62
Added Info GLASS AUDIO 4/1999 (v.11#4) pg. 60

Pilot AA-901 classic triode amplifier schematic features a Williamson design.
GLASS AUDIO 1/1999 (v.11#1) pg. 62

Western Electric theater amplifier schematic illustrates the use of interstage transformers.
GLASS AUDIO 1/1999 (v.11#1) pg. 67

A different SRPP (shunted regulated push-pull) circuit replaces the resistor between the upper and lower valve with a coil.
GLASS AUDIO 1/1999 (v.11#1) pg. 68

Triode power amplifier uses both 6C33C-B and 12AU7 vacuum tubes and shunt-regulated push-pull (SRPP) design.
GLASS AUDIO 2/1999 (v.11#2) pg. 1
Added Info AUDIOXPRESS Dec 2002 (v.33#12) pg. 40 (Improved design)

SV572-10 push-pull amplifier. Step-by-step through the design, component selection, and construction of a push-pull amp based on the SV572 output vacuum tube.
GLASS AUDIO 2/1999 (v.11#2) pg. 16
Correction GLASS AUDIO 4/1999 (v.11#4) pg. 57
Added Info GLASS AUDIO 5/1999 (v.11#5) pg. 70

An expandable beginner's vacuum tube audio amplifier project. Both the amp and the power supply have only six parts each.
GLASS AUDIO 2/1999 (v.11#2) pg. 38
Added Info GLASS AUDIO 4/1999 (v.11#4) pg. 62
Added Info GLASS AUDIO 6/2000 (v.12#6) pg. 60

Theory of the SRPP circuit. Theoretical analysis conducted to establish the principle formulas governing the shunted regulated push-pull (SRPP) circuit behavior.
GLASS AUDIO 2/1999 (v.11#2) pg. 44
Added Info GLASS AUDIO 5/1999 (v.11#5) pg. 66

A different triode power amplifier circuit which is unique, safe, and stable for driving low-mu power triodes.
GLASS AUDIO 2/1999 (v.11#2) pg. 50
Added Info GLASS AUDIO 3/1999 (v.11#3) pg. 46 (Using tubes with filamentary cathodes)
Added Info GLASS AUDIO 5/1999 (v.11#5) pg. 68
Added Info GLASS AUDIO 4/2000 (v.12#4) pg. 62
Added Info AUDIOXPRESS Jan 2001 (v.32#1) pg. 101
Added Info AUDIOXPRESS Aug 2001 (v.32#8) pg. 26 (Circlotron amp configuration)
Added Info AUDIOXPRESS Mar 2002 (v.33#3) pg. 61 (Circlotron amp configuration)

Single-ended (SE) amplifier circuit which uses a 300B vacuum tube, but no exotic parts or expensive interstage transformers.
GLASS AUDIO 2/1999 (v.11#2) pg. 69

LW6-180 amplifier. Design of a high-quality Class AB2 audio amp that produces 180-watts mono, bridge or balanced input, and 90+90W stereo. Utilizes the 18TU output transformer and the 6LW6 high-perveance beam power tube.
GLASS AUDIO 3/1999 (v.11#3) pg. 16

New push-pull tube amplifiers. Designs for 21st century tube-type amplifiers which take advantage of new inventions and new toroidal output-transformer technologies.
GLASS AUDIO 3/1999 (v.11#3) pg. 34

Constructing a simple single-ended amplifier utilizing the Svetlana 6BM8 vacuum tube.
GLASS AUDIO 3/1999 (v.11#3) pg. 74

A push-pull monaural amplifier incorporates well-matched Svetlana SV6550C tubes and Pliatron toroidal transformers with a fine-tuned voltage-driver circuit having simulated circuit parameters and stabilized screen-grid bias of the output tubes.
GLASS AUDIO 4/1999 (v.11#4) pg. 1
Added Info GLASS AUDIO 1/2000 (v.12#1) pg. 58

Redesigning (upgrading) the Dynaco Mark VI amplifier circuit to eliminate problems with the 8417 and 7199 vacuum tubes.
GLASS AUDIO 4/1999 (v.11#4) pg. 34
Correction GLASS AUDIO 6/1999 (v.11#6) pg. 68

Schematic for the Eico HF-86 stereo power amplifier.
GLASS AUDIO 4/1999 (v.11#4) pg. 68

70-watt per channel low-distortion amplifier project utilizes the 6L6GC vacuum tube.
GLASS AUDIO 5/1999 (v.11#5) pg. 1
Correction GLASS AUDIO 1/2000 (v.12#1) pg. 58
Added Info GLASS AUDIO 1/2000 (v.12#1) pg. 62
Added Info GLASS AUDIO 2/2000 (v.12#2) pg. 62

How to build a push-pull stereo 4.3-watt amplifier requiring only three recycled vacuum tubes.
GLASS AUDIO 5/1999 (v.11#5) pg. 32
Added Info GLASS AUDIO 2/2000 (v.12#2) pg. 66

6AS7 amplifier. Reviving C.G. McProud's classic push-pull amplifier design (circa 1948) using today's components.
GLASS AUDIO 6/1999 (v.11#6) pg. 20
Added Info AUDIOXPRESS Jan 2001 (v.32#1) pg. 101, 105
Added Info AUDIOXPRESS Jul 2001 (v.32#7) pg. 87
Added Info AUDIOXPRESS Nov 2001 (v.32#11) pg. 83

Designing your own amplifier. Part 1. Voltage amplifier stages.
GLASS AUDIO 6/1999 (v.11#6) pg. 48

12-watt high-quality amplifier circuit (circa 1959).
GLASS AUDIO 6/1999 (v.11#6) pg. 76

One more 91A. An attempt to duplicate the classic Western Electric 91A monoblock amplifier using original WE parts and engraved base WE 300B power triodes.
GLASS AUDIO 1/2000 (v.12#1) pg. 1

A universal phase splitter which you can add to a push-pull audio amplifier for better performance.
GLASS AUDIO 1/2000 (v.12#1) pg. 32
Added Info GLASS AUDIO 5/2000 (v.12#5) pg. 54

Designing your own amplifier. Part 2. The power stage.
GLASS AUDIO 1/2000 (v.12#1) pg. 50

Berning ZH270 power amplifier. A detailed review of an interesting technology used in a 70W/channel vacuum-tube audio amplifier. Part 1. Design theory. Features a zero-hysteresis approach to the output-transformerless problem.
GLASS AUDIO 1/2000 (v.12#1) pg. 22

SV572-10 single-ended triode power amplifier features a relatively simple design with high-quality listening performance. Includes instructions for winding the special output transformers.
GLASS AUDIO 2/2000 (v.12#2) pg. 1

A basic 50W stereo system. Part 1. Building the 50W monoblock tube amplifier.
GLASS AUDIO 2/2000 (v.12#2) pg. 24
Added Info GLASS AUDIO 5/2000 (v.12#5) pg. 50
Added Info AUDIOXPRESS Mar 2001 (v.32#3) pg. 77

Berning ZH270 power amplifier. A detailed review of an interesting technology used in a 70W/channel vacuum-tube audio amplifier. Part 2. Component makeup, measurement tests and listening tests.
GLASS AUDIO 2/2000 (v.12#2) pg. 34

Designing your own amplifier. Part 3. Phase inverters.
GLASS AUDIO 2/2000 (v.12#2) pg. 48

General advice on audio amplifiers using the 807 beam power tube.
GLASS AUDIO 2/2000 (v.12#2) pg. 67
Added Info GLASS AUDIO 5/2000 (v.12#5) pg. 50
Added Info AUDIOXPRESS Jan 2001 (v.32#1) pg. 97 (Bogen HO-125)
Correction AUDIOXPRESS Apr 2001 (v.32#4) pg. 82 (Bogen HO-125)
Added Info AUDIOXPRESS Sep 2001 (v.32#9) pg. 80, 81 (Bogen HO-125)

A vintage cathode-follower circuit (circa 1952) for a vacuum-tube amplifier.
GLASS AUDIO 2/2000 (v.12#2) pg. 70

100W triode mono amplifier is very stable and has low distortion throughout the audio spectrum to its full output. Uses Hammond transformers and rugged Sveltana 6550 vacuum tubes. Est. cost: $500.
GLASS AUDIO 3/2000 (v.12#3) pg. 1
Added Info AUDIOXPRESS Jan 2001 (v.32#1) pg. 96 (Corrections and a time-delay circuit)
Added Info AUDIOXPRESS Mar 2001 (v.32#3) pg. 82
Added Info AUDIOXPRESS Oct 2001 (v.32#10) pg. 81

Designing your own amplifier. Part 4a. Push-pull power stages.
GLASS AUDIO 3/2000 (v.12#3) pg. 36

Harmonic cancellation capabilities of the SRPP (shunt-regulated push-pull) circuit.
GLASS AUDIO 3/2000 (v.12#3) pg. 42

An affordable SE triode amplifier. Est. cost: $100.
GLASS AUDIO 4/2000 (v.12#4) pg. 1
Added Info AUDIOXPRESS Mar 2001 (v.32#3) pg. 84

Review of the Assemblage SET-300B, an 8W RMS per channel single-ended triode (SET) stereo power amplifier kit from Sonic Frontiers International. Est. cost: $800.
GLASS AUDIO 4/2000 (v.12#4) pg. 38

Basic 50W stereo system. Part 3. A solid-state subwoofer amplifier.
GLASS AUDIO 4/2000 (v.12#4) pg. 42

Designing your own amplifier. Part 4b. Push-pull power stages (continued).
GLASS AUDIO 4/2000 (v.12#4) pg. 52

Schematic for the vintage Acrosound Model Ultra-Linear II amplifier (circa 1959).
GLASS AUDIO 4/2000 (v.12#4) pg. 70

A 20W amplifier. Low-cost vacuum tube stereo amplifier that is completely self-contained. Est. cost: $260.
GLASS AUDIO 5/2000 (v.12#5) pg. 20
Correction GLASS AUDIO 6/2000 (v.12#6) pg. 62
Added Info AUDIOXPRESS Apr 2001 (v.32#4) pg. 87, 88
Added Info AUDIOXPRESS Jun 2001 (v.32#6) pg. 80
Correction AUDIOXPRESS Oct 2001 (v.32#10) pg. 85

A hybrid amp revisited. Prototype amplifier circuit features a tube, interstage transformer, and power MOSFETs.
GLASS AUDIO 5/2000 (v.12#5) pg. 30

Review of the AE-25 Super Amp push-pull stereo power amplifier kit from Audio Electronic Supply. Rated for 25W ultralinear or 15W triode-connected. Est. cost: $1000.
GLASS AUDIO 5/2000 (v.12#5) pg. 33

An SE 6AS7G design. This single-ended amplifier design makes use of paralleled 6AS7G tubes.
GLASS AUDIO 5/2000 (v.12#5) pg. 42

SV300B SE stereo amplifier uses Plitron single-ended toroidal transformers.
GLASS AUDIO 6/2000 (v.12#6) pg. 1
Correction AUDIOXPRESS Jun 2001 (v.32#6) pg. 82

Designing your own amplifier. Part 5. Feedback amplifiers.
GLASS AUDIO 6/2000 (v.12#6) pg. 30

The Tradition. Design for a triode-based single-ended amplifier features high-power and low-distortion.
GLASS AUDIO 6/2000 (v.12#6) pg. 48

Direct vs. parallel feed output in single-ended triode amplifiers.
GLASS AUDIO 6/2000 (v.12#6) pg. 58
Added Info AUDIOXPRESS Aug 2001 (v.32#8) pg. 72

Electronic crossover circuit and an optional power-amplifier setup for a complete biamp project.
HANDS-ON ELECTRONICS Summer 1984 (v.2#1) pg. 77

Low-power audio amplifier circuit. Operated on supplies from 1.8 up to 12 volts.
HANDS-ON ELECTRONICS Spring 1985 (v.2#4) pg. 36

Simple, easy-to-build amplifier circuit has several useful applications, ranging from audio amplification to electronic troubleshooting. Est. cost: $7.
HANDS-ON ELECTRONICS Jan-Feb 1986 (v.3#1) pg. 59

Audio power-amplifier circuit built around the Sanyo STK084 thick-film hybrid amplifier module. Capable of 50 watts of output power with only 0.05% distortion.
HANDS-ON ELECTRONICS Jul-Aug 1986 (v.3#4) pg. 43

Circuit for a portable amplifier for use with a "Walkman" tape player or radio. Uses the earphone output to drive a small speaker.
HANDS-ON ELECTRONICS Dec 1986 (v.3#7) pg. 42

Designing audio amplifiers using op-amp building blocks. Includes a BASIC computer program to make the job easier.
HANDS-ON ELECTRONICS Dec 1986 (v.3#7) pg. 86

Schematic diagram for a small power amplifier with a 140x voltage gain. Maximum output is 100 mW (with an 80-ohm speaker) up to 600 mW (with an 8-ohm speaker).
HANDS-ON ELECTRONICS Jan 1987 (v.4#1) pg. 110

Schematic diagram of a small amplifier that can convert a transistor radio from earphone to loudspeaker operation.
HANDS-ON ELECTRONICS Jan 1987 (v.4#1) pg. 111
Correction HANDS-ON ELECTRONICS Sep 1987 (v.4#9) pg. 4

Mini-stereo amplifier circuit is powered by two 9-volt batteries.
HANDS-ON ELECTRONICS May 1987 (v.4#5) pg. 96

Circuit for a high-impedance buffer to be installed between an audio amplifier and additonal loads.
HANDS-ON ELECTRONICS Jul 1987 (v.4#7) pg. 94

All-purpose amplifier circuit is suitable for an AM or FM tuner, small phonograph, CPO add-on, etc.
HANDS-ON ELECTRONICS Sep 1987 (v.4#9) pg. 95

Servicing high-wattage audio amplifiers. Most troubleshooting requires only a pocket VOM or DMM.
HANDS-ON ELECTRONICS Oct 1987 (v.4#10) pg. 67

Simple amplifier circuit for use with a turntable.
HANDS-ON ELECTRONICS Oct 1987 (v.4#10) pg. 94

Amplifier circuit for a turntable is capable of driving a 6" speaker with its 1-watt output.
HANDS-ON ELECTRONICS Dec 1987 (v.4#12) pg. 100

Simple amplifier circuit can be used with small radios, tape recorders, record players, or as a PA amplifier. Power with a six-volt lantern battery or nine-volt transistor-radio battery.
HANDS-ON ELECTRONICS Feb 1988 (v.5#2) pg. 85

Utility audio amplifier circuit offers a voltage gain of about 200 with a 0.4-watt output. Add-on circuits also shown.
HANDS-ON ELECTRONICS Aug 1988 (v.5#8) pg. 93

Adding a monophonic center channel to your stereo amplifier. est. cost: $5 plus speaker.
MECHANIX ILLUSTRATED #460 Sep 1966 (v.62) pg. 82

Installing a solid-state stereo amplifier in one of two speakers.
MECHANIX ILLUSTRATED #489 Feb 1969 (v.65) pg. 101

Inexpensive, easy-to-build stereo amplifier can develop 25 watts per channel, or 35 watts per channel if larger power transformer is substituted. Frequency response rated from 20 cycles to 70,000 cycles per second. Has provisions for accepting inputs from phono, tuner, tape and auxiliary sources.
MECHANIX ILLUSTRATED #536 Jan 1973 (v.69) pg. 66

How to build a basic hi-fi amplifier with a rating of 3.5 watts. Est. cost: $15.
MECHANIX ILLUSTRATED #545 Oct 1973 (v.69) pg. 27

A versatile audio amplifier chip. How to use the popular LM386 IC in a variety of applications, including (1) low-gain amplifier, (2) high-gain amplifier, and (3) oscillator.
MODERN ELECTRONICS [2] Jun 1985 (v.1#9) pg. 62

Test bench audio amplifier. Delivers 400 mW of power into an 8-ohm speaker. Powered from 117-volt ac line or +12 battery.
MODERN ELECTRONICS [2] Oct 1985 (v.2#4) pg. 56

Audio amplifier experiments. Includes construction of a simple audio amplifier, underwater hydrophone, light-sensor/amplifier combinations, and a basic "photophone" system.
MODERN ELECTRONICS [2] Apr 1986 (v.3#4) pg. 66

Experimenting with the power MOSFET (MOS field-effect transistors). Includes circuits for a simple audio amplifier, linear lamp dimmer, pulse-driven light dimmer, lamp flasher, and timer circuits.
MODERN ELECTRONICS [2] Aug 1986 (v.3#8) pg. 64

Solid-state audio circuits. Part 1. Basic circuits used in audio-amplifying equipment. Both discrete transistor and integrated-circuit audio amplifier circuits are explored.
MODERN ELECTRONICS [2] Sep 1986 (v.3#9) pg. 16

Digital stereo amplifier. A state-of-the-art basic stereo power amplifier features pulse-width-modulation design to produce distortionless high-power output. Outputs 100 watts or more per channel. Est. cost: $149.
MODERN ELECTRONICS [2] Dec 1987 (v.4#12) pg. 18
Correction MODERN ELECTRONICS [2] May 1988 (v.5#5) pg. 7
Added Info MODERN ELECTRONICS [2] Sep 1988 (v.5#9) pg. 7

Experimenting with audio circuits. Using op-amps to build a variety of professional audio circuits to suit different requirements.
MODERN ELECTRONICS [2] Mar 1988 (v.5#3) pg. 34

Speaker overload indicator alerts listener to speaker signal input problems that can damage the transducers. Monitors your amplifier for (1) too much output, (2) too much distortion and (3) too much positive or negative dc voltage.
MODERN ELECTRONICS [2] Dec 1988 (v.5#12) pg. 34
Correction MODERN ELECTRONICS [2] Feb 1989 (v.6#2) pg. 7

Switching amplifier. A 60-watt, dual-channel, nonlinear, Class-D amplifier project.
POPTRONIX HOBBYISTS HANDBOOK Winter 1996 pg. 13

Hi-fi interlock.
POPULAR ELECTRONICS [1] Aug 1964 (v.21#2) pg. 49

Transistorized audio amplifier circuit for demonstration purposes.
POPULAR ELECTRONICS [1] Aug 1964 (v.21#2) pg. 78

Three-watt output transistor amp has audio range of 30-20,000 cycles.
POPULAR ELECTRONICS [1] Oct 1964 (v.21#4) pg. 69

Schematic for transistorized audio amplifier.
POPULAR ELECTRONICS [1] Nov 1964 (v.21#5) pg. 117

Two-transistor all-purpose audio amplifier.
POPULAR ELECTRONICS [1] Dec 1964 (v.21#6) pg. 68

General purpose transistor audio amplifier circuit is good for intercom, signal tracer, etc.
POPULAR ELECTRONICS [1] Feb 1965 (v.22#2) pg. 77

Transistor audio amplifier circuit without usual driver transformer.
POPULAR ELECTRONICS [1] Mar 1965 (v.22#3) pg. 74

Stereo amplififer uses two compaction tubes and has 5-watt output.
POPULAR ELECTRONICS [1] Jul 1965 (v.23#1) pg. 43

Solid state push-pull 6-watt audio amplifier for $10.
POPULAR ELECTRONICS [1] Nov 1965 (v.23#5) pg. 73

Amplifier circuit delivers up to 100 watts into an 8-ohm load when driven by an external pre-amplifier with an output of 0.1 to 1.0 volt RMS.
POPULAR ELECTRONICS [1] Mar 1966 (v.24#3) pg. 80

Circuit for a complete audio power amplifier. Made up of only three transistors and no other components.
POPULAR ELECTRONICS [1] Oct 1966 (v.25#4) pg. 85

Circuit for a 4-transistor audio amplifier powered by a 12-volt battery.
POPULAR ELECTRONICS [1] Dec 1966 (v.25#6) pg. 74

Solid-state 70-watt amplifier for mono or stereo hi-fi sound systems. Unit is able to deliver most of its full quality sound at all volume levels. Harmonic distortion less than 1%. Frequency response is 5Hz to 25Hz (within 1 dB). Est. cost: $35 per channel.
POPULAR ELECTRONICS [1] Feb 1967 (v.26#2) pg. 41

Multipurpose FET signal tracer. Can be used as a millivoltmeter, output meter, microphone preamplifier, auxiliary audio amplifier, tape recorder monitor, etc., as well as a sensitive signal tracer.
POPULAR ELECTRONICS [1] Apr 1967 (v.26#4) pg. 43

Solid-state line-operated audio amplifier. Uses a field-effect transistor (FET) that will give you the high impedance needed for crystal or ceramic cartridge.
POPULAR ELECTRONICS [1] Jun 1967 (v.26#6) pg. 40

L'il Tiger stereo power amplifier. Puts out 18 watts per channel r.m.s. with 8-ohm speakers. Supply voltage can be anything from 12 to 45 volts depending on output power desired. Speaker ratings from 3.2 to 16 ohms. Est. cost: $10 to $25.
POPULAR ELECTRONICS [1] Dec 1967 (v.27#6) pg. 29

Six circuits using linear integrated circuits including circuits for (1) remote control amplififer, (2) wide-band amplifier and limiter, (3) A 1-watt audio amplifier, (4) a subminiature audio amplifier, (5) a half-watt audio amplifier, and (6) bifet amplifier.
POPULAR ELECTRONICS [1] Dec 1967 (v.27#6) pg. 49

Half-watt audio amplifier circuit has 67 dB gain and a frequency response from 16 Hz to over 60 KHz.
POPULAR ELECTRONICS [1] Feb 1968 (v.28#2) pg. 77

A 20-watt audio amplifier circuit developed by Motorola.
POPULAR ELECTRONICS [1] Jun 1968 (v.28#6) pg. 69

Audio amplifier circuit using two field-effect transistors which produces the same effect as using a pentode.
POPULAR ELECTRONICS [1] Aug 1968 (v.29#2) pg. 78

Treble and bass tone control circuits which may be used in almost any amplifier.
POPULAR ELECTRONICS [1] Aug 1968 (v.29#2) pg. 85

Basic 3-tube mono amplifier capable of delivering 3 or 4 watts.
POPULAR ELECTRONICS [1] Sep 1968 (v.29#3) pg. 67

One- or two-watt amplifier uses an integrated circuit designed for audio circuits. Est. cost: $8.
POPULAR ELECTRONICS [1] Jan 1969 (v.30#1) pg. 47

Two high-quality 40 or 100-watt power audio amplifiers that match the FET stereo preamplifier featured in the May 1969 issue.
POPULAR ELECTRONICS [1] Jul 1969 (v.31#1) pg. 51

Circuit changes to improve the low-frequency response of a basic two-stage amplifier.
POPULAR ELECTRONICS [1] Aug 1970 (v.33#2) pg. 89

Assembling a universal "Tiger" hi-fi power amplifier with 125 watts per channel design.
POPULAR ELECTRONICS [1] Oct 1970 (v.33#4) pg. 31

Stereo amplifier outputs 18 watts per channel using integrated circuit coupled to a pair of output transistors. Est. cost: $38.
POPULAR ELECTRONICS [1] May 1971 (v.34#5) pg. 49

Circuit for a 35-watt universal audio system.
POPULAR ELECTRONICS [1] Jun 1971 (v.34#6) pg. 86

Stereo amplifier produces 30 watts per channel into 8 ohms. Similar in design to the Universal Tiger 80 watt unit featured in the October 1970 issue. Est. cost: $55.
POPULAR ELECTRONICS [1] Oct 1971 (v.35#4) pg. 27

A 15-watt amplifier built around the Sinclair model Z30 audio amplifier module (costing $16).
POPULAR ELECTRONICS [1] Dec 1971 (v.35#6) pg. 59

Circuit for a simple, low-cost amplifier that delivers 1/4 watt into a speaker of 15 ohms.
POPULAR ELECTRONICS [1] Apr 1973 (v.3#4) pg. 100

Build an audio power amplifier which does not have either an output transformer or an output capacitor. Unit delivers 3 to 5 watts rms output power to an 8-ohm load. Response is flat form 10 Hz to 20,000 Hz. Est. cost: $20.
POPULAR ELECTRONICS [1] Nov 1973 (v.4#5) pg. 44

Three-transistor audio amplifier can have either audio or r-f inputs.
POPULAR ELECTRONICS [1] Jan 1974 (v.5#1) pg. 68

Ampzilla, a super-power, high-fidelity stereo amplifier with 200 watts per channel at 8 ohms and low distortion. Est. cost: $340.
POPULAR ELECTRONICS [1] Sep 1974 (v.6#3) pg. 33

The TITAN modular stereo power amplifier. Choose 25, 50 or 80 watts per channel into 8 ohms, both channels driven. Unit uses plug-in power modules, a transformer and one PC board with only a few components. Est. cost: $200.
POPULAR ELECTRONICS [1] Jun 1975 (v.7#6) pg. 27

A look at integrated circuit audio amplifiers for the hobbyist.
POPULAR ELECTRONICS [1] Aug 1975 (v.8#2) pg. 78

A high-power mobile stereo amplifier provides 15-watts per channel from a 12-volt dc power supply. Can be converted for 6-volt dc use. Est. cost: $25.
POPULAR ELECTRONICS [1] Feb 1976 (v.9#2) pg. 50

A look at the National Semiconductor IC type LM389. Supplied in an 18-pin DIP, the device is composed of three uncommited npn transistors and a low-power integrated audio amplifier in a single package. Might be usable in AM & FM receivers, walkie-talkies, tape recorders, toys, games...etc. Circuits for a phono amplifier and tape recorder are shown.
POPULAR ELECTRONICS [1] Sep 1976 (v.10#3) pg. 92

The LM380 power amplifier integrated circuit. Has a very low output impedance and can be directly connected to an 8-ohm speaker. Can operate up to 3.7 watts with heat sink. Circuits for amplifier, intercom and phase-shift oscillator shown.
POPULAR ELECTRONICS [1] Sep 1976 (v.10#3) pg. 121

Circuit for a low-power audio amplifier to boost signal from a crystal set.
POPULAR ELECTRONICS [1] Feb 1977 (v.11#2) pg. 77

A description of what the various classes of audio amplifier circuits (A,B,C,D, or G) mean to today's audiophile.
POPULAR ELECTRONICS [1] Mar 1977 (v.11#3) pg. 74

Add a clipping indicator to your audio amplifier. This circuit senses power supply voltages and flashes a warning LED just before the onset of clipping. Use to help prevent damage to speakers.
POPULAR ELECTRONICS [1] Nov 1979 (v.16#5) pg. 75

Cancel rumble with this bass-summing amplifier. May also be used an as an electronic crossover for a subwoofer power amplifier.
POPULAR ELECTRONICS [1] Apr 1981 (v.19#4) pg. 77

Speaker amplifier circuit is designed to plug into the earphone jack of Walkman-type receivers and provide enough power to drive external speakers.
POPULAR ELECTRONICS [2] Feb 1989 (v.6#2) pg. 25
Added Info POPULAR ELECTRONICS [2] Dec 1989 (v.6#12) pg. 4

Cassette/radio booster provides a voltage gain of 20 dB (10 times) for driving a larger external speaker.
POPULAR ELECTRONICS [2] Mar 1989 (v.6#3) pg. 28

Simple class-A audio-amplifier circuit utilizes a power hexFET.
POPULAR ELECTRONICS [2] May 1989 (v.6#5) pg. 85

Line-powered audio amplifier circuit is isolated from the AC power source by a 24-volt, center-tapped transformer.
POPULAR ELECTRONICS [2] Jul 1989 (v.6#7) pg. 26

Build a 30-watt monophonic audio amplifier for use in an intercom, PA system, etc. Build two for stereo use. Est. cost: $16.
POPULAR ELECTRONICS [2] May 1990 (v.7#5) pg. 61

Audio power amplifier can be used to boost an audio signal so it can be heard in a high-noise environment.
POPULAR ELECTRONICS [2] Oct 1990 (v.7#10) pg. 81

Build this 20-watt stereo amplifier for an automobile- or home-stereo receiver. It utilizes a pair of TDA2004 integrated amplifiers.
POPULAR ELECTRONICS [2] Jul 1991 (v.8#7) pg. 40

Op-amp based circuits. (1) One-way voice-activated intercom. (2) Analog audio-frequency meter. (3) Simple audio-power amplifier.
POPULAR ELECTRONICS [2] Apr 1992 (v.9#4) pg. 67

Audio amplifier circuits. (1) Bird-feeder monitor. (2) Ear protector disables amplifier if output volume exceeds a preset level. (3) Variable-frequency audio oscillator. (4) Very-low frequency whistler receiver.
POPULAR ELECTRONICS [2] Oct 1993 (v.10#10) pg. 72

Circuit for a 2-watt amplifier converts a "Walkman" to a small-room stereo system.
POPULAR ELECTRONICS [2] Dec 1994 (v.11#12) pg. 31
Added Info POPULAR ELECTRONICS [2] Jul 1995 (v.12#7) pg. 30
Added Info POPULAR ELECTRONICS [2] Oct 1995 (v.12#10) pg. 72

Build a breadboard vacuum-tube audio amplifier to demonstrate the sound-quality difference between tubes and transistors.
POPULAR ELECTRONICS [2] Jan 1995 (v.12#1) pg. 53
Added Info POPULAR ELECTRONICS [2] Apr 1995 (v.12#4) pg. 4
Added Info POPULAR ELECTRONICS [2] Jun 1995 (v.12#6) pg. 4

Simple single-transistor circuits. (1) Voltage regulator outputs 6-volts DC. (2) Constant-current output. (3) Simple audio amplifier. (4) Impedance-matching circuit. (5) LED-control circuits turn either off or on in the presence of a DC voltages from 5- to 9-volts. (6) Relay-driver circuit has a latching feature that keeps the relay on once energized.
POPULAR ELECTRONICS [2] Dec 1995 (v.12#12) pg. 77

Build a single-ended hi-fi amplifier which uses three vacuum tubes. Est. cost: $110 (kit).
POPULAR ELECTRONICS [2] Feb 1996 (v.13#2) pg. 38

Build a 60-watt, dual-channel, nonlinear switching amplifier.
POPULAR ELECTRONICS [2] Apr 1996 (v.13#4) pg. 30
Correction POPULAR ELECTRONICS [2] Jun 1996 (v.13#6) pg. 6
Correction POPULAR ELECTRONICS [2] Sep 1996 (v.13#9) pg. 6

Stereo amplifier circuit is a low-power unit for a Walkman, Discman, or similar device.
POPULAR ELECTRONICS [2] Jul 1996 (v.13#7) pg. 66

20-watt push-pull audio amplifier circuit that uses 2 Darlington transistors.
POPULAR ELECTRONICS [2] Jul 1997 (v.14#7) pg. 65
Correction POPULAR ELECTRONICS [2] May 1998 (v.15#5) pg. 57

One-chip power amplifier circuit is suitable for use with any portable audio application (PA system, intercom, CD player, etc.).
POPULAR ELECTRONICS [2] Jul 1997 (v.14#7) pg. 66

Mini-CD player stereo amplifier circuit works better than commercially available power amplifiers. Also features tone controls.
POPULAR ELECTRONICS [2] Aug 1997 (v.14#8) pg. 64

Stereo power amplifier circuit provides up to 7-watts per channel. Circuit for a companion preamp is also shown.
POPULAR ELECTRONICS [2] Aug 1997 (v.14#8) pg. 65, 66

Amplifier for a portable CD player which is designed to deliver 4 watts of power per channel into an 8-ohm load.
POPULAR ELECTRONICS [2] May 1998 (v.15#5) pg. 39
Correction POPULAR ELECTRONICS [2] Jul 1998 (v.15#7) pg. 5

Circuit for a single-stage audio amplifier that uses two 60FX5 vacuum tubes.
POPULAR ELECTRONICS [2] Jun 1998 (v.15#6) pg. 28
Added Info POPULAR ELECTRONICS [2] Sep 1998 (v.15#9) pg. 67

200-watt audiophile amplifier. Build a high-power MOSFET amplifier that can form the basis of a home-stereo or subwoofer system, musical-instrument amplifier, PA system, or any custom audio project. Est. cost: $162 per channel (kit).
POPULAR ELECTRONICS [2] Sep 1999 (v.16#9) pg. 29
Correction POPULAR ELECTRONICS [2] Nov 1999 (v.16#11) pg. 15

Auxiliary amplifier and speaker for transistor radios.
POPULAR MECHANICS Jan 1964 (v.121#1) pg. 196

Build a booster amplifier to get more sound from a small transistor radio.
POPULAR MECHANICS Jul 1978 (v.150#1) pg. 95

Its easy to build electronic projects with prewired modules. Put these high-gain amplifier modules to work in (1) an intercom, (2) an audio signal tracer, and (3) a stereo amplifier.
POPULAR SCIENCE Oct 1967 (v.191#4) pg. 140

Matched transistor pairs in audio amplifiers. A discussion of why they are necessary and how to service them when one goes bad.
RADIO-ELECTRONICS Dec 1977 (v.48#12) pg. 66

How to troubleshoot amplifiers made in Japan which use transistors, but do not have voltage information printed on the schematics. Includes a chart for determining voltage drop across the emitter resistor.
RADIO-ELECTRONICS Feb 1978 (v.49#2) pg. 68

Buyer's guide to hi-fi amplifiers.
RADIO-ELECTRONICS May 1979 (v.50#5) pg. 47

Build this super audio amplifier. Bridge-type power output uses cheap transistors and simple power supply. Delivers from 60 to 100 watts RMS depending on power supply. Est. cost: $35 per channel less power supply.
RADIO-ELECTRONICS Dec 1979 (v.50#12) pg. 55
Added Info RADIO-ELECTRONICS Jun 1980 (v.51#6) pg. 24

Applications of Fairchild's microamplifier integrated circuit (uA 783). Use in child's phonograph, TV audio output, guitar amplifier, etc.
RADIO-ELECTRONICS Nov 1980 (v.51#11) pg. 78

Speaker overload protector circuit for lower-priced amplifiers.
RADIO-ELECTRONICS Dec 1981 (v.52#12) pg. 92
Correction RADIO-ELECTRONICS Aug 1982 (v.53#8) pg. 24

How to improve audio amp performance.
RADIO-ELECTRONICS Jun 1982 (v.53#6) pg. 67

How to design analog circuits. Audio power amplifiers. Part 1. A look at some practical circuits using both bipolar and FET devices.
RADIO-ELECTRONICS Mar 1983 (v.54#3) pg. 73

How to design analog circuits. Audio power amplifiers. Part 2. Practical audio power-amplifier circuits.
RADIO-ELECTRONICS May 1983 (v.54#5) pg. 81

Two general-purpose amplifier circuits to boost low-voltage outputs from keyboards, microphones, etc.
RADIO-ELECTRONICS Apr 1984 (v.55#4) pg. 45

Two low-power audio amplifier IC's (ULN-3705M and ULN-3784B) are viewed.
RADIO-ELECTRONICS Oct 1984 (v.55#10) pg. 100

Build this high-power FET stereo amplifier. Part 1. Uses power MOSFET output transistors in a complementary configuration. Delivers 250 watts/channel into a 4- or 8-ohm load.
RADIO-ELECTRONICS Dec 1984 (v.55#12) pg. 43

High-power FET audio amplifier. Part 2. Construction details.
RADIO-ELECTRONICS Jan 1985 (v.56#1) pg. 59
Correction RADIO-ELECTRONICS Mar 1985 (v.56#3) pg. 20

Audio overload protection circuits.
RADIO-ELECTRONICS Jan 1985 (v.56#1) pg. 89

Custom-tailored audio. Tremolo add-on circuit for an amplifier, electronic musical instrument, or any other audio circuit.
RADIO-ELECTRONICS Sep 1985 (v.56#9) pg. 96

"Walkman" amplifier. Build this versatile amplifier and get home stereo sound from your "Walkman"-type cassette player or radio. Est. cost: $22.
RADIO-ELECTRONICS Mar 1986 (v.57#3) pg. 59, 79

High-power FET (field-effect transistor) stereo amplifier delivers a conservatively-rated 95 watts (rms) per channel at eight ohms with distortion that is less than 0.02%. Est. cost: $300. Part 1. Circuit theory.
RADIO-ELECTRONICS Jun 1986 (v.57#6) pg. 63
Added Info RADIO-ELECTRONICS Nov 1986 (v.57#11) pg. 12

High-power FET stereo amplifier. Part 2.
RADIO-ELECTRONICS Jul 1986 (v.57#7) pg. 56

High-power FET stereo amplifier. Part 3.
RADIO-ELECTRONICS Aug 1986 (v.57#8) pg. 57, 64, 67

Design procedure for a simple transistor amplifier to solve an audio-gain problem. Includes a BASIC computer program for calculating component values.
RADIO-ELECTRONICS Aug 1987 (v.58#8) pg. 55
Correction RADIO-ELECTRONICS Dec 1987 (v.58#12) pg. 26

Need to keep a load on the output of a vacuum-tube amplifier power supply is explained.
RADIO-ELECTRONICS Dec 1987 (v.58#12) pg. 23

Micro-sized amplifier can be built using either SMD (surface-mount devices) or conventional components. SMD version fits on PC board under 1"x1". Use it for both a home-brewed "Big-Ear" type microphone and a super snooper. Est. cost: $20.
RADIO-ELECTRONICS Aug 1988 (v.59#8) pg. 33, 67

High-power hi-fi audio stereo amplifier project for your home or car. Uses an IC capable of pumping out 100-watts RMS of audio into 4-ohms. Est. cost: $149 plus power supply ($100-$119).
RADIO-ELECTRONICS Mar 1989 (v.60#3) pg. 51, 74, 77, 78
Correction RADIO-ELECTRONICS Apr 1989 (v.60#4) pg. 14
Correction RADIO-ELECTRONICS May 1989 (v.60#5) pg. 16
Added Info RADIO-ELECTRONICS Nov 1989 (v.60#11) pg. 22

Working with audio power amplifier IC's. Building amplifier circuits for audio applications.
RADIO-ELECTRONICS Mar 1990 (v.61#3) pg. 52

Tip on adding resistance to a transistorized audio amplifier's output stage in order to mimic the high output impedance (and resulting sound) of a vacuum-tube amplifier.
RADIO-ELECTRONICS Apr 1991 (v.62#4) pg. 80

Solid-state audio amplifier. Drive a 4- to 16-ohm speaker with 4.5- to 6-volt battery power. Est. cost: $6.
RADIO-TV EXPERIMENTER #772 Feb-Mar 1966 (v.20#1) pg. 83

An 8" speaker with its own amplifier and power supply boosts the quality of sound from inexpensive, low-power cassette players, etc.
SCIENCE & ELECTRONICS [1] Oct-Nov 1970 (v.28#5) pg. 57

Combo-Amp, a combination microphone preamplifier, line amplifier, and volume level meter. Enables you to control tape recorder or P.A. volume level from the microphone position.
SCIENCE & ELECTRONICS [2] Mar-Apr 1981 (v.21#2) pg. 73

How to choose a stereo amplifier. What is the meaning of class A, AB, D, E,... as applied to amplifiers and how many watts of power you actually need.
SCIENCE & MECHANICS Spring 1978 pg. 65

Sub-bass power boosting and other applications using the LM12 monolithic power operational amplifier. Circuit for a booster which provides the additional low-frequency power boost of a third amplifier to augment the power output in the sub-bass range.
SPEAKER BUILDER 4/1988 [Jul 1988] (v.9#4) pg. 22
Correction SPEAKER BUILDER 6/1988 [Nov 1988] (v.9#6) pg. 63
Added Info SPEAKER BUILDER 1/1989 [Jan 1989] (v.10#1) pg. 54

An easy IC power amp/crossover is used to add a subwoofer to a low-power stereo or to a video system.
SPEAKER BUILDER 2/1989 [Mar 1989] (v.10#2) pg. 33

More power for less. 20 watt power amplifier with power supply is built from parts available at Radio Shack. Est. cost: $35 per channel.
SPEAKER BUILDER 1/1991 [Feb 1991] (v.12#1) pg. 36
Added Info SPEAKER BUILDER 1/1992 [Jan 1992] (v.13#1) pg. 72, 73
Correction SPEAKER BUILDER 2/1992 [Apr 1992] (v.13#2) pg. 68

Schematic for a power amplifier that utilizes the TDA1514AU amplifier chip.
SPEAKER BUILDER 3/1994 [Apr 1994] (v.15#3) pg. 49
Added Info SPEAKER BUILDER 7/1994 [Oct 1994] (v.15#7) pg. 56
Added Info SPEAKER BUILDER 2/1995 [Mar 1995] (v.16#2) pg. 64

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