[Lowfer] S-51 Interesting Puzzle

[Michael Sapp]

Dex & All:   Upon closer inspection of the S-51 schematic, the output transformer wiring shows the 6V6 using the entire transformer primary impedance for the plate load and the 35L6 using the center tap for the plate load. Checking the tube specs for Class A self bias, the 35L6 shows 2.5K plate load and the 6V6 with a 5K ohm plate load, so that is consistent with the wiring arrangement. So there is more screen V drop on the 6V6 with its higher plate load value. Both tubes use the same cathode and grid bias resistors....

http://i1296.photobucket.com/albums/ag19/wa3tts/S51A_zps96487ddf.jpg

My Hallicrafters S-22R, circa 1940, similarly feeds the DC B+ to the screen which is tied to the plate of the audio output tetrode (a 25L6) through the primary of the audio output transformer.  I bounced this observation over to a TV engineer acquaintance, whose comment was that it would appear to be a good feedback method to limit distortion on audio peaks.....

73, Mike wa3tts