[R-390] R: Strange variation of sensitivity AGC resistance toward the chassis

[N4BE_Jim--- via R-390]

For what it's worth, in restoring my SW radio, I found it more expedient to just "shotgun" replace every capacitor touching the AGC, especially in the RF deck.  The .005 mfd bypass caps throughout the RF deck were completely replaced with modern caps.  Didn't bother wasting time trying to isolate specific caps.  With the age of these radios you can safely assume they all leak.

Also check all resistor values. They typically drift with age.

And I can't emphasize enough the problems induced by spraying switch wafers with any kind of cleaner.  It's best to individually clean each contact wiper with a Deoxit pen.  If you spray the phenolic wafers, they will absorb the chemical and will no longer be high impedance.  And for the same reason, never lubricate the antenna trimmer phenolic shaft.  The trimmer cap is connected to the AGC line.

73 Jim N4BE

Sent from my iPad

> On May 8, 2015, at 5:57 PM, r-390-request at mailman.qth.net wrote:
> 
> R: Strange variation of sensitivity AGC resistance toward the chassis