[R-390] R-390 sideband adapter

[DJED1 at aol.com]

I certainly agree.   In the 70s I bought several CV-591s ($35 each from 
DOD-wish I had kept them as an investment), which helped, but they didn't have a 
convenient speaker output, and took up a lot of space on the desk.   I tried my 
own version of Dallas' AVC mod, and the audio driven version.   However, none 
were really satisfactory without a product detector, and so I built the 
solid-state product detector and external fast attack AVC.   The AVC voltage is 
derived from the IF output, and only requires a couple of transistors and diodes.  
 The AVC characteristic is not as flat as my R4C, but the R390 was never 
specified to have a real flat AVC characteristic.   I can listen to widely 
different signal strengths now without any distortion.
I've been pretty happy with it, although my BFO is not as stable as the 
internal BFO.   I picked up a couple of BFO crystals which I will add to the unit 
one of these days.
Ed