[R-390] R-390 Woes

[Renee K6FSB]

Adam-
I have had issues in mine with the postage stamp caps C550 and 551 see 
if shorted. 180 and 100 pf respectively.
The hum issue is sometimes a fil to cathode issue, sub a different 12au7 
V507, V510 (normal culprits)
easy simple AGC mod is add two diodes (langford mod) R556 and R557, AGC 
works just like an A, Larry Haney made some improvements for the A.
but get everything working first.
oh one other problem was one of the shielded cables in the chassis, it 
was shorted IIRC due to damage.
So, check the harness too.
one more thing to note in the AGC section of the IF deck R554 may be 470 
ohm. I finally found an IF deck with a 2.2k (per schem)
apparently it was a never noted anywhere in a change order. so 470 is 
ok. was discussed in R390 reflector (pg107 in a download IF tips?)
Renée



On 10/7/25 1:55 PM, Adam Morehouse wrote:
> Hey guys,
>
> I appreciate the pointers on my R-392, and now that it's buttoned up, it's
> time to work on my R-390. I only tested this briefly when I first got it,
> today I threw it up on the bench. Supposedly this was restored by Rick
> Mish, it is very clean (except the gear train, which has a lot of fresh
> grease...), and the front panel is pristine.
>
> It does pull stations, but the volume is extremely low in AGC mode, and
> gets slightly louder when placed into MGC.
>
> In MGC, with the BFO switched on, it plays at a normal (not super loud, but
> loud) volume.
> In AGC, with the BFO switched on, it hums, low volume audio.
>
> The limiter seems to have no effect, and varying the BFO doesn't do
> anything at all no matter AGC/MGC.
>
> I have Tom's solid state kit installed, and B+ at the AF deck test point is
> a steady 180.5vdc.
>
> I am going to dig out the TM's later on, I have them somewhere...but maybe
> somebody here can help point me in the right direction.
>
> Thanks!
>
> Adam K2AAM
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