[R-390] Bfo problem help .

[Flowertime01 at wmconnect.com]

Takis,

Did this problem start happening in a receiver that you have been using daily?

Is this a problem you now have in a receiver that you have just started to 
use after it has been setting turned off for a few months or more?

Different problems with different things to look at.

Turn the lights off and look for a tube glowing blue in the IF or audio deck.
A gassy tube will distort.

Has your receiver had the plastic caps removed? These old plastic caps leak 
and cause distortion.

Run the receiver in MGC and AGC functions. Does it distort equally in both 
modes?
The AGC circuits can cause distortion.

The R390 does not do SSB all that wonderful to begin with. Are you sure you 
also do not have distortion in AM mode? CW is a beat at the BFO against any 
signal. You mostly do not get distortion of the CW tone through the audio deck.

>From your report, it sounds as if its time to test all the tubes in the 
receiver. 
One had gone over the edge and some more are likely close to the edge.

Most likely it is just a tube problem. Any where in the chain. 

A tube gets marginal in emission with use. Then it gets all kinds of spurs. 
Mixers, and oscillators will get spurs. These extra spurs then mix up with all 
the good stuff and the audio output sounds poor. The tubes in the IF deck 
while not mixers will also produce lots of extra products. Tube bias will fall off 
the linear part of its curve and leave the tube operating on a knee. The 
stage will then produce poor output sounds because every thing is not getting 
equal treatment within the tubes stage.

With the questions in mind, tell us a bit more about the problem and we can 
try to get specific for you.


Roger L. Ruszkowski AI4NI




   </HTML>