Two Thordarson advertising flyers from May and June 1939, numbers SD-378D and SD-389D featuring a "Multi-Band Transmitter," and an "Amateur Speech Amplifier." Both include schematic drawings and parts lists, which make them of interest and usefulness for those who wish to study any and all pre-WW II vacuum tube base-band and RF circuits.
The base-band circuits are especially interesting for they illustrate over modulation control and peak limiting.
The schematic drawings are squeezed into the 8.5 x 11 inch sheets. In order to render them with a high enough resolution to be clear at 200% magnification (for my middle aged eyes), a large file size was unavoidable. I apologize for that but hope the usefulness will outweigh the inconvenience (you only have to download it once).
Pages 1 and 2: New! "Multi-Band" Transmitter by THORDARSON (SD-378D 5/39)
Instantaneous Band-Switching from Front of Panel
Radio Frequency Unit 2 x 6L6G 1 x TZ40
Modulator Unit 2 x 6L6
Pages 3 and 4: Amateur Speech Amplifier by THORDARSON (SD-389D 6/39)
The Most Complete and Versatile Speech Amplifier Ever Offered to the Amateur
Choice of Three Circuits
Peak Limiting Circuit -- Overmodulation Control Circuit -- Conventional Circuit
1 x 6F5 1 x 6L7 1 x 6C5 2 x 2A3 1 x 6R7(pk.lim.)
[schem.1 with over-modulation control; schem.2 Peak limiting amp.]
4 pages, 6 Mb.
http://home.fnal.gov/~atkinson/thordarsonflyers1939.pdf
