[R-390] agc repair

Sat, 17 Apr 2004 00:54:17 -0400

Hi Gene,
I've fixed three "no AGC" problems and none involved leaky caps or tubes,
although the former can certainly degrade AGC action.

The one that was toughest to find but easiest to fix was a 390A that acted
like the AGC line was shorted to ground but the resistance measurements
looked OK. The problem was that one side of the diversity OR-ing diode on
the rear terminal had been bent over and was touching the chassis, so it was
clamping the AGC line to within a few tenths of volts to ground!

The other two problems each occurred in a 390 and 390A IF module. The Zxxx
coil that is the resonant plate load for the AGC amplifier tube opened up
and thus the poor tube wasn't getting its B+. Had to replace that coil in
each IF. :^(

73,
John

----- Original Message ----- 
From: "Gene Dathe" <[email protected]>
To: <[email protected]>
Sent: Sunday, April 11, 2004 3:14 PM
Subject: [R-390] agc repair

> The Agc on my 390-A doesn't work.  Substituted V506, V508 and V509 with
new
> tubes, no help.  No agc voltage appears at TB102 3 and 4.  Any thoughts on
> where to start?
>
> Thanks, Gene  NA�G
>