[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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