[R-390] R-390a modified IF sub-chassis

[Larry H]

Gary,  Capt. Lee's implementation switched the audio after the noise limiter stage.  This is very similar to his original except it switches the audio before the limiter, thus providing noise limiting in SSB mode.  In AM mode, the required bias is provided to the limiter circuit through the negative diode load voltage.  However, in SSB mode an alternative method must be provided.  There are 2 pieces in this schematic.  Part of it is from the rectified 25.2 vac creating a fixed negative voltage.  The second and variable part is that provided by the mystery module, obtaining its input from the diode load voltage.
In theory this would work, but I have no way of knowing.  If it were mine, I'd try it and see.  Remember, with this  mod on, this IF is not interchangeable with other R-390A's.
Regards, Larry