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 worldradiohistory.com (formerly americanradiohistory.com) scans. scans. Articles marked ♠ are from an unknown source.

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Rice & Kellogg 1925 Notes on the Development of a New Type of Hornless Loud Speaker - From the Transactions of the A.I.E.E. An evaluation of existing loud speaker technologies, then the development of of a wide-range, high quality loud speaker - now known as the "dynamic" loud speaker. Interesting discussion section. Thanks to Charlie DeLuca for donating the article to be scanned.

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.

Wheeler 1946 An Analysis of Three Self-Balancing Phase Inverters * - Analysis of the paraphase, long-tailed pair, and cathodyne phase splitters.

Builder 1946 Effect of Negative Voltage Feedback on Power Supply Hum in Audio-Frequency Amplifiers * - A look at the effect of feedback on hum in audio amplifiers.

Furst 1946 Periodic Variations of Pitch in Sound Reproduction by Phonographs * - An analysis of turntable wow plus a description of a wow-meter.

Maxwell 1947 Dynamic Performance of Peak-Limiting Amplifiers * - A detailed look at the behavior of peak-limiting amplifiers (also known as compressors) of various types.

Krauss 1948 Class-A Push-Pull Amplifier Theory - Comparing push-pull and parallel operation of triodes running in class A, push-pull operation is shown to give the most power at lower distortion.

Hopkins & Stryker 1948 A Proposed Loudness-Efficiency Rating for Loudspeakers and the Determination of System Power Requirements for Enclosures - A very detailed analysis, both theory and experiments, by Bell Labs on measuring loudspeaker efficiency and calculating power needed in various scenarios.

Warren & Hewlett 1948 An Analysis of the Intermodulation Method of Distortion Measurement - A theoretical analysis of the intermodulation (IM) distortion test methodology, a comparison with total-harmonic-distortion testing, and a way of predicting IM distortion from amplifier characteristics.

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.

McKenzie 1948 Stereophonic Sound - An early demonstration of stereo by Marvin Camras of the Armour Research Foundation. Three-track tape recording is used.

Camras 1949 A Stereophonic Magnetic Recorder - A complete stereophonic playback system using both two and three channels is described. Various microphone and speaker placements are evaluated. Conclusion: for home use, two channels are sufficient. A more detailed analysis than the 1948 McKenzie article. Quite advanced for 1949!

Goldmark et al 1949 The Columbia Long-Playing Microgroove Recording System * - The technical trade-offs made in implementing the LP microgroove record - one of the most successful standards ever.

Corrington & Kidd 1951 Amplitude and Phase Measurements on Loudspeaker Cones * - How careful analysis of cone motion can be used to diagnose various quirks and anomalies in loudspeaker drivers.

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.

Sterling 1951 Extended Class-A Audio * - By paralleling a triode-connected 807 with a tetrode-connected 807, an amplifier with the efficiency of beam tetrodes and the linearity of triodes is produced, without resorting to class-B operation.

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.

Peterson & Sinclair 1952 A Single-Ended Push-Pull Audio Amplifier * - A new audio output topology that allows output-transformerless designs. Commercialized by later Philips and the basis for most solid-state power amplifiers.

Bachman 1952 The Application of Damping to Phonograph Reproducer Arms * - The mechanics behind tone-arm damping.

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.

Snow 1953 Basic Principles of Stereophonic Sound - A very comprehensive review of all aspects of stereo reproduction. Since this was published in the Journal of the SMPTE, this article likely influenced the adoption of stereo in the film industry.

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.

Walker 1955 Wide Range Electrostatic Loudspeakers Part 1 *
Walker 1955 Wide Range Electrostatic Loudspeakers Part 2 *
Walker 1955 Wide Range Electrostatic Loudspeakers Part 3 * - A three-part article on the design of electrostatic speakers. The author, Peter Walker of the Acoustical Manufacturing Co., Ltd., would come out with the QUAD electrostatic speaker in 1957.

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.

Leak & Sarkar 1956 Full-Range Electrostatic Loudspeakers * - A different implementation of an electrostatic speaker, with a fixed perforated plate with conductive diaphrams on each side.

Lin 1956 Quasi-Complementary Transistor Amplifier * - One of the first descriptions of the quasi-complementary output stage, which was used extensively up through the 1970s, before complementary power transistors became available. Modest performance, but this was very early in the development of germainium transistors.

Davis & Frayne 1958 The Westrex Stereodisk System - The history of and description of the stereophonic disc recording system we use today. Also described are the original recorder (cutting head) and reproducer (cartridge). Historically important.

Corrington & Murakami 1958 Tracing Distortion in Stereophonic Disk Recording - An analysis using a digital computer of the distortion due to tracing distortion in both the 45°-45° (Westrex) system and the vertical-lateral system.

Bernard 1958 Distortion in Audio Phase Inverter and Driver Systems - Distortion measurements on a variety of driver circuits. Result coorelate with my own findings: octal is better than miniature and the 6AN8 (and similar tubes) suck.

Zenith 1960 Extended Stereo System * - An article from Electronics World that describes Zenith's use of matrixing the L+R and L-R signals in a stereo phonograph to reduce or enhance the stereo effect. The matrixing extends to the output stage, where a push-pull amplifier supplies the L+R and a single-ended amplifier mixes-in the L-R signal.

Dinsdale 1974 Horn Loudspeaker Design-1 *
Dinsdale 1974 Horn Loudspeaker Design-2 *
Dinsdale 1974 Horn Loudspeaker Design-3 * - A three-part article on the design of horn loudspeakers. Theory plus two examples.

Belcher 1978 A New Distortion Measurement * - Measuring distortion by using a pseudo-random noise and a comb filter. Listening tests show much better correlation between the distortion number and perceived distortion.

Baxandall 1980 Audio Gain Controls * - A two-part article by Peter Baxandall describes the sublties of implementing gain controls of audio amplifiers.

Antoniazzi et al 1981 Measuring Transient Intermodulation in Audio Amplifiers * - In 1970, Otala described a new kind of distortion: Transient Intermodulation distortion (TIM). This article from Wireless World describes a different way of measuring TIM.

Hephaistos La distorsion thermique (FR) - [found on the web] An article from the French magazine L'Audiophile describes the distortion in time caused by signal-induced shifts in the operating points of bipolar transistors, sometimes called "thermal tails". Tests showing this effect are presented. This is an important and often overlooked effect, and IMHO one of the causes of "solid-state sound". No date but likely the mid-to-late 1980s.