[R-390] R 390A RF Deck problem

DJED1 at aol.com DJED1 at aol.com
Fri May 15 19:34:41 EDT 2009


Hmmm- it sounds to me like you've tracked it down to the need for an  
alignment.  If changing the tubes makes no difference, and the problem  travels 
with the RF deck, it sounds like it either needs an alignment, or a  tuning 
cap has gone bad.  Have you checked the sensitivity on all bands, so  that 
you can  determine if it is one particular set of transformers that  need 
work?  Note that the RF is broken down into octave bands, so you just  need to 
check somewhere in the bands .5-1, 1-2, 2-4, 4-8, 8-16, and   16-32.
My experience with sensitivity tests is to determine the signal level at  
which there is a 10 dB change in audio output when a 30% modulation is 
switched  on and off (this seems to be the standard for the radio).  I get a  
sensitivity of about 0.5 microvolts, although the mil-spec only calls for 2 or  
3. 
Let us know what you find out.
Ed
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