[R-390] R-390a Audio Improvement

[Tony Casorso]

Hi everyone,

I just wanted to my experience with the R-390a audio out here for 
informational purposes. I was unhappy with the audio. I had made the audio 
deck cap changes that Chuck Rippel recommends to improve audio and I was 
still unhappy. Finally I removed the diode load link from the back of the 
set and connected my audio generator to the inbound side of the link. 
Monitoring the line out with my scope I saw that the low end rolled off 
about 3db between 600 and 700 Hz. This is way higher than the published 
audio curve. I checked all caps and resistors in the audio deck and 
everything was fine. Finally I decided to replace C549 at the limiter output 
in the IF deck with a .1uf  (it was .01). The audio improvement was 
dramatic. The .01 cap had already been replaced by me with a brand new mylar 
back when I got the receiver. The low end rolls off now between 100 and 
200Hz.

Tony