[Amps] I like to think there are no stupid questions

[Michael Tope]

Great idea, Jim. I think Ameritron did this on some of their amps. I saw 
a picture of one recently that had a spark gap on the tune cap.

I was recently bringing a 30L-1 back to life and was having problems 
with arcing in the tune capacitor. The rotor plates were a little off 
center, which made the problem worse. After adjustment the capacitor 
breaks down around 3200V which is reasonably close to what you would 
expect with 45 mil plate spacing. Still it would be nice to have a spark 
gap in there.

73, Mike W4EF................

On 8/19/2024 11:28 AM, jim.thom jim.thom at telus.net wrote:
> Date: Mon, 19 Aug 2024 07:17:31 -0600
> From: Tom Hellem <tom.hellem at gmail.com>
> To: Mark - N5OT <r-emails at n5ot.com>
> Cc: Amps <amps at contesting.com>
> Subject: Re: [Amps] I like to think there are no stupid questions
>
>
> <My LC800 was arcing and tripping out.
> <Turned out to be the plate tuning cap.
> <Once they start arcing it's tough to fix em. Tried filing and cleaning up
> the carbon tracks, <but eventually ended up replacing it with a vac
> variable.
> <That amp uses 3 x  3cx800A7's.
> <I figured it was abused by the previous owner.
> <I realize this doesn't exactly answer your question, but might save you
> some grief in case <you have the same thing going on.
>
> <Tom
> <K0SN
>
> This is why I advocate installing a simple, adjustable spark gap across the
> tune cap...
> (which also protects the bandswitch) and a 2nd spark gap across the load
> cap.  These are easily made from brass 6-32 / 8-32 / 10/32 /  1/4-20
> hardware.  I use brass acorn nuts, which face each other.  The acorn nuts
> are semi domed....and easily replaced if they get trashed.  Brass nuts /
> flat washer's etc are used to lock the gap.... sorta like the adjustments
> on a vibroplex keyer paddles. Box store items.
>
> Then the gap is set such that the gap will arc before the tune and load
> caps arc.  Either feeler gauges used and / or a hi-pot tester.
>
> I also install a a pair of adjustable spark gaps on my hb amps, that use
> vac tune and vac load caps.  If an issue with say a TR relay, connector,
> wrong ant, no ant, etc,  you don't want 1.5 kw going into a wide open =
> infinite swr = load cap welded shut asap.  If you think trying to fix an
> air variable cap is a bitch, try fixing an air variable load cap.  A
> bandswitch is also a bitch to replace.
>
> Save yourself some grief.
>
> Jim  VE7RF
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