An 8877 can arc and burn away a small point where it arced and be ok after
that. But this usually happens with a new tube.
If the grid was over heated it could happen.
Good luck with it
Gary k4FMX
Gary Schafer
> On Feb 15, 2026, at 3:33 PM, Steve Bookout, NR4M <steve@nr4m.com> wrote:
>
> 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@k3lr.com> wrote:
>>
>> AC mains "brown out"?
>>
>> 73
>> K3LR
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Gary Schafer
>> Sent: Sunday, February 15, 2026 3:53 PM
>> To: Steve Bookout
>> Cc: amps@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@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
>>>
>>>
>>>
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>>
>>
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