[R-390] AGC Problem Returns

[Dennis Wade]

Good Morning,

      After finding (I thought) the problem with my AGC in the 390A,
it seems now to have returned.  To recap the original problem briefly:

           Observed low no signal voltage on the line (just about 0,
maybe slightly negative) instead of the spec'ed -0.4.  Replaces V509
and no signal condition became as spec'ed.  Noticeable improvement in
audio quality.

     Then I proceed to do a full alignment with very good results. 
Radio burns in on the bench.  Problem develops.

    Now:  No-signal AGC is back near 0, at about -0.08 to -0.10. 
Noticeable distortion, especially on very strong signals.  AGC only
develops about -7 volts on the strongest BCB signal (>80 on the
carrier meter).

        Sounds like something is loading it again.  My question is
more how to isolate it to a particular stage.  If I look at the signal
grids of all the controlled tubes (IF and RF decks), will the
offending stage be obvious, or will all the grids look the same since
they are all on the controlled line.  And, is it correct that if I'm
looking at a low resistance on the AGC line, that I can isolate it to
the RF or IF deck by pulling the IF connector and observing what if
any change.

       Would the components around V509 be likely suspects?

       And probably the most elementary of all:  I've been assuming
that the resistances given in the voltage/resistance diagrams are with
the module in question fully connected to the rest of the
radio...right?

          Just looking for some hope..I'm hoping I don't end up
digging for capacitors in the IF deck.  :(
                    Thanks for any advice.  Sign me "Trying not to
whine in Carmichael."...

                             Dennis
-- 
Dennis L. Wade
KG6ZI
Carmichael, CA