[Amps] AL-1500 'thump'

[maflukey at gmail.com]

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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