[R-390] R-390a AGC Issue/Observation

[David Wise]

I believe in this case that the positive voltage is
correct AGC Delay operation, coming from B+ via R544.

Dave Wise

-----Original Message-----
From: Jim M. [mailto:jmiller1706 at cfl.rr.com] 
Sent: Monday, April 13, 2009 5:20 PM
To: David Wise; 'Tony Casorso'; R-390 at mailman.qth.net
Subject: RE: [R-390] R-390a AGC Issue/Observation

I don't know if this was mentioned yet, but an AGC controlled tube with a
"leaky" gris can cause the grid voltage to tend toward positive as I recall.
This can mess up the AGC line.  Check all the AGC controlled tubes for grid
leaks if your tube tester does that.  Or just trial-and-error replace tubes.
Another thing that can happen is if you get oil on the antenna trip shaft,
on the fiber insulating clamp.  The antenna trim capacitor is on the AGC
line.  If you get oil or lubricants on that fiber clamp, it will show
resistance to ground and affect AGC performance.