[AMPS] ALPHA 78A HELP

[Turkisher Dan-CSLC82]

I have an Alpha 78A...works fine on all bands, BUT: On 20 meters in BANDPASS
mode there is internal arcing (frying noise). In MANUAL TUNE, the amp tunes
fine with no arcing. This with 50-100W drive into 50 ohm load.

Internal inspection didn't reveal anything obvious. There is some carbon
(maybe?) on the wire from the PHONE/CW switch that goes to chassis ground.
This could just be coincidence and contamination...the wire is not burned
and there are no other signs of arcing. I did redress the wire so it is well
away from the tuning capacitors.

Any ideas/suggestions on how to troublehsoot?

Thanks and 73

Dan
K0DAN

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