Hello Matt,
I was wrong about the soft start. It IS in the AL-1500.
My mistake was I asked ‘AI’.
On the schematic, it’s obviously there (K3 and a 10 ohm R).
Steve NR4M
Sent from my iPhone
> On Feb 15, 2026, at 8:45 PM, maflukey@gmail.com wrote:
>
> Hi Steve,
>
>>> '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.<<
>
> Did you remove the soft start relay and inrush resistor? How old are
> your PS caps and are they original or upgraded?
>
> Matt,
> KM5VI
>
>
>
> -----Original Message-----
> From: Amps <amps-bounces@contesting.com> On Behalf Of Steve Bookout
> Sent: Sunday, February 15, 2026 12:39 PM
> To: amps@contesting.com
> Subject: [Amps] AL-1500 'thump'
>
> 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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