[R-390] Correction To "Chambers Audio Derived AGC Mod"

[Dan Merz]

Hi,  well,  I wondered why it didn't work and was pursuing the cause.  I found the mentioned RS rectifier in my junk box,  still in the orig. package,  probably 20 years old.  But I got no effect with your described hookup - I'll try the corrected
version shortly.

But aside from that I found another quirk ??  in my 390a.  I've never been happy with agc on the set - it has the two diode mod in the agc circuit.  I began to wonder if the C551 cap was bad and tried the suggested test of switching between fast,
med and slow setting to see if the indicated carrier level changed as an indication of leakage..  In doing this I noticed the quirk?? - when I switched from slow ( which has B+ on one side of C551) to med or fast ,  the carrier meter pins to the
upscale direction then drifts back to a level that is about 20 db higher.  It stays at this level until I turn the rf gain down and back up,  then it goes back to the lower level,  about 20 db down from where it went went it drifted down from the
meter pinned state.  While all this is going on,  I put a VTVM on the agc line and don't see this happening with the agc voltage.  It didn't reflect this quirk,  except it did go far upscale negatively when I switched from slow to med but returned
to a level that was the same as before the switch.  It there some kind of latching of the i.f. tube on the other side of the carrier meter,  or is this likely a bad carrier meter.  It seems to do it regardless of what the signal carrier strength is
and shows no quirks when I move it up and down with the rf gain control.  When I switch from fast to med to slow,  in that order,  the carrier level stays the same.  Only when I switch back up to med or fast does the quirk occur,  Dan.

Dallas Lankford wrote:

> Well, I don't know how I botched it so badly.  The 10K ohm resistor should be 1K ohms.  And instead of being in the path to the AGC line, it is in one (either one) of the AC lines of the bridge rectifier to either one of the LINE OUT terminals.
>
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