Here are scanned articles from various audio or other technical journals, listed chonologically. Unless otherwise noted, these scans were done by John Atwood. Articles marked "*" were extracted from americanradiohistory.com scans. Articles marked ♠ are from an unknown source.
Riley 1927 A New Era in Push-Pull Amplification - An early amplifier using push-pull type 71 tubes and battery power supplies.
Millen 1928 An A.C. Phonograph Amplifier - James Millen describes an AC-operated push-pull amplifier - not easy, since battery-type tubes are used. Note that the speaker connects directly to the push-pull plates, implying a high-impedance speaker.
Barcus 1933 Designing and Constructing Direct-Coupled A.F. Amplifiers - A two-part article on direct-coupled audio power amplifiers. Choke-loading is used on the driver stages. This is not the Loftin-White circuit, but is the topology of Jack Eliano's "Direct Reactance Drive" amplifier (see Vacuum Tube Valley issue 14, page 25).
Hollister 1933 Quality in Audio Amplifiers - Two different amplifiers using the 2B6 direct-coupled class A2 tube. The second circuit is bi-amped - a separate amplifier for the woofer and tweeter.
Klipsch 1945 Woofer-Tweeter Crossover Network * - A cross-over using a modified plate transformer in a push-pull 2A3 amplifier.
Hadfield 1948 Amplifier Load Impedance Reduction * - Using a special operating point for a pentode class-A amplifier to give low output impedance. An example of a 50 ohm, 10 Watt single-ended design is given.
Hollmann 1951 Boucherot Compensation * - Using an R-C network to cancel the reactive part of a load. The example given is cancelling a speaker's reactive load in a single-ended pentode amplifier.
Mitchell 1951 Audio Amplifier Damping * - Explains the meaning of damping factor and how it is increased by negative feedback. This article does not go into the variable damping circuits seen in some amplifiers of this time.
Fletcher & Cooke 1951 Cathode-Follower Loudspeaker Coupling - An OTL (Output TransformerLess) amplifier. Massive overkill design for 6 watt output. Check out the four 872A rectifiers in the power supply! There are comparisons against various output transformers. Attached are letters to the editor regarding this amp from March and May 1952.
Williamson 1952 The Williamson Amplifier - Reprints from Wireless World on the famous Williamson amplifier. The articles range from 1947 to 1952. This is the original British booklet, not the reprint by Old Colony, so the advertisements are the original British ones.
Bereskin 1954 High Quality High Efficiency Power Amplifier - A 50-watt amplifier using beam power tubes in class B. Lots of circuit ideas here.
Kiebert 1954 System Design Factors for Audio Ampifiers - An analysis of the design factors and tube choices for push-pull amplifiers. Several designs presented, most using class AB2.
Mitchell 1955 Effect of the Cathode Capacitor on P-P Output Stage ♠ - Experiments run on a class-A Williamson amplifier with and without a cathode bypass capacitor across the common cathode resistor of the output stage. Results are somewhat inconclusive, but tend to favor the capacitor. My own observation: an unbypassed common cathode resistor makes the push-pull stage more like a differential amplifier with current limiting. This current limiting supresses the peak current when transistioning to class B operation.