[R-390] Re: AGC Failure Apparently Solved...

[Mike Melland]

Several weeks ago many of you responded in ansewr to a 
problem I was having with my "new" Motorola R-390A.  The 
problem was failure of the AGC (distortion) in any filter 
position on a strong signal after the set warmed up.  The 
AGC voltage was way off the values in the manual.

I started checking tubes and found none that were 
obviously bad in the AGC circuit.  I removed and 
substituted with known good tubes all of the IF section 
tubes and the problem persisted. After several days I also 
decided after speaking with Roy Morgan to try the tubes on 
the RF side including the 6DC6.  I removed the shields, 
removed and replaced all the tubes after socket cleaning 
and turned the rig on to warm it up until the problem 
resurfaced as it always did as the radio warmed up. 
 Well... it's been over two weeks and the problem hasn't 
surfaced again.  The AGC voltages remain steady and within 
the range the manual states they should be.

Apparently.... a tube I believe got jostled loose in 
transit to me and would go intermitent when warmed up.  I 
wonder if a tube pin/socket wasn't seated well and the 
socket got warm and the metal expanded causing the 
problem. 


--
Michael Melland, W9WIS
Winneconne, WI USA