[R-390] Local & Line potentiometers

[Charles Steinmetz]

Craig wrote:

>Resistance wasn't quite up to snuff. Wires go to correct 
>terminations, no shorts, no grounds, etc.

If the end-to-end resistance of each pot is between 1k and 10k, they 
should work fine.  They do not appear to be your trouble.

>With a speaker connected to either audio circuit, knob at zero, at 
>times the RF gain has to be decreased to save the ears. IF gain is 
>set correct, -7volts @ 150 micro-volts.  Transformer used to match 
>impedance, speaker to receiver.

Either you have WAY too much audio at the CW ends of R104 and 105, or 
you have a ground problem at the pots (CCW ends not firmly grounded), 
or BOTH audio amps (V602A/V603 and V602B/V604) are broken.  The 
chance of both audio amps being broken is slim, so that's the least 
likely.  Using a scope, check for audio at the CCW ends of the pots 
(terminal 3 of R104 and R105) to rule that out.  There should be no 
more than a millivolt or so of audio there.

If these check OK (and I expect they will), then you have WAY too 
much audio coming from the detector/limiter/first audio amp and 
follower.  That would suggest an AGC problem.

>Could a person just add a resistor where the wire from S104 
>(connection 4) and the wire from P120 meet? If my memory is correct, 
>this point is on the line gain pot and easy to access.

There is something broken.  Find out what it is, and fix it.  Don't 
hide the problem by modifying the radio.

Best regards,

Charles