[Amps] AL-1500 'thump'

[Gary Schafer]

Sounds like the tube arcing.

73
Gary K4FMX
Gary Schafer


> On Feb 15, 2026, at 12:40 PM, Steve Bookout <steve at 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
> 
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps