Sounds like the tube arcing.
73
Gary K4FMX
Gary Schafer
> On Feb 15, 2026, at 12:40 PM, Steve Bookout <steve@nr4m.com> wrote:
>
> Hello all,
>
> Had a friend using the station this weekend, and while sitting there with
> him, while operating on 40 meters, we both heard a 'thump' or 'thungg' from
> the amp while transmitting. Happened two or three times or a period of a few
> hours.
>
> Reminded me of the sound the current surge makes when you first turn the HV
> on in an amp.
>
> Puzzling to me cuz if that was it, why and why now? And, no other follow up
> issues. I don't think a PS filter cap would 'sorta, kinda' short, then not
> and be OK. It would only be a small part of a larger 'event'. (Been there;
> done that and still remember the pucker factor.)
>
> Amp was being operated in a typical fashion, with resonant load, 25 watts of
> drive, ~ 40 ma grid current, +/- 1200 watts RTTY.
>
> Dealt with many amps before, but have not heard anything like this in the
> past. 'If' it had a soft start to deal with initial current surge, I might
> think there was a problem there, but there isn't one.
>
> Ideas?
>
> 73 Steve NR4M
>
>
>
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