[Milsurplus] R-392 Audio Module Oscillation - The Solution

[Al Klase]

I want to thank everyone who weighed in on this problem.

John, W4NET, knew the fix.  In radios with the 26A7 tube, there is an 
8.2-meg resistor connected to pin 5 of T603, the audio output 
transformer secondary.  This resistor provides global negative feedback 
to the grid of the first audio amp, V606.  Unfortunately, the 
solid-state module introduces an additional 180-degree phase shift 
making that positive feedback.

Remove the audio-IF deck and cut the lead to R629 (8.2-meg).  The 
solid-state module has it's own internal feedback loop.

When you look at this drawing,
(http://www.roveroresearch.org/r392/r392_ss_audio.gif ) You'll notice 
R629 is absent.  I have to assume radios built with the solid-state 
agree with this schematic.  This explains the rumors of modules working 
in some sets and not others.

BTW, the audio sounds clean, and there's plenty of it.  I guess I should 
have expected that from a Western Electric design.

VY 73,
Al