[Amps] AL-1500 'thump'

[Steve Bookout, NR4M]

Good suggestion, but don’t think so.  Solid AC line and nothing dimmed.  Computer would have reset. 
Didn’t see any type of glitch from the amp meters as I was facing the amp. 
The other fellow, Gary, mentioned tube arcing.  Surely, could be that.  I can pull the tube and hi-pot it. Unless, some really marginal voltages before a fault, that might not tell me much. 
I’ve got several tubes and I could swap one out, but does not PROVE anything.  With this tube, I may never see it happen again. 
Of course, I’d love to never see this become a REAL problem.  It would really define the problem, but may not be good for the equipment. 
I had a Millen HV connector arc over 20 years ago.  The problem was easy to find, but it took months to find all the damage it caused. 
I appreciate you and Gary sharing your thoughts. 

Steve NR4M 
Sent from my iPhone

> On Feb 15, 2026, at 4:08 PM, Tim Duffy <k3lr at k3lr.com> wrote:
> 
> AC mains "brown out"?
> 
> 73
> K3LR
> 
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Gary Schafer
> Sent: Sunday, February 15, 2026 3:53 PM
> To: Steve Bookout
> Cc: amps at contesting.com
> Subject: Re: [Amps] AL-1500 'thump'
> 
> 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
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>