[Amps] AL-1500 'thump'

[Steve Bookout, NR4M]

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 at 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 at contesting.com> On Behalf Of Steve Bookout
> Sent: Sunday, February 15, 2026 12:39 PM
> To: amps at 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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