The insulating coatings suggested are not going to solve the primary
issue which is high RF voltages developed in the tank circuit.
since you are running out of inductance that suggests that the amp's
tank is not designed to support 12m operation and since 12M was
not even allocated when the amp was built any 12M operation is a
bonus. You might want to contact Henry Radio about suggested
modifications as they still support their old amps even though they do
not build them any longer.
The arcing is eventually going to blow expensive components like
bandswitches, tubes and caps
John Becker wrote:
> I recently bought a used Henry 3K Premier. Something arcs when I tune it
> up only on 12M and only with the HV switch in the SSB position. I
> removed the cover to take a look and found that the rotary inductor was
> exactly one turn from minimum. This placed the rotary contact in close
> proximity to the termination at the end of the winding. I tried running
> the amp briefly with the cover removed to visually confirm that this was
> where it was arcing. Unfortunately, removing the cover affected the
> tuning, and when retuned there was no arcing but neither was the rotary
> contact in proximity to the end contact anymore.
>
> Unless someone has a better suggestion, I'm going to apply an insulating
> coating to the termination area at the end of the inductor to see if
> that fixes the problem. I can use either "Q Dope" or "Corona Dope". "Q
> Dope" is intended for RF circuits and shouldn't have any effect on the
> inductance or Q of the circuit, but may not have sufficient insulating
> capabilities. "Corona Dope" is intended for high voltage circuitry in
> television receivers, but might not be as good a choice for an RF
> circuit. My gut feeling is that I should use the "Corona Dope" because
> it will be applied to less than one inch of the inductor and therefore
> should have a minimal effect on the inductance or Q. On the other hand,
> the increase in breakdown voltage required to fix the problem may not be
> very much and the "Q Dope" might be adequate. Opinions, anyone? Thanks!
>
> 73,
>
> John, K9MM
>
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