I have found that, once an arc occurs in the air-variable plates of a PA
tuning cap, it just continues to melt along the edges and cause more and
more arcing by virtue of the "slag" that the arc leaves behind on the plate.
A very careful hour spent filing with an automotive point file and a
magnifying glass cured the problem in my L4-B last year. I drive that amp
full bore with an Omni V...no problems since.
Gud DX, All --
Mitch Alexander KG9DB
> From: Seay[SMTP:DELJAN@worldnet.att.net]
> Sent: Friday, December 11, 1998 3:11 PM
> To: firstname.lastname@example.org; email@example.com
> Subject: Re: [TenTec] VI+ Key Up Spike
> It would help to know what you mean by " Blew the
> main tuning cap" Air variable caps, even though they
> have arced, are still fine. Even if a carbon path has
> developed, it can be cleaned out. And the cap remains
> good. My guess is high circulating current is the problem.
> As to the spike - I've watched mine carefully and there
> is NO Leading Edge Spike, and I would doubt seriously
> that any do. The threads on actual spikes have been
> referencing the FT-1000 series of transceivers.
> The OMNI-6 has a very steep leading edge, causing
> what most people would call hard or harsh keying, but
> I don't think any I have heard of had a spike, which indicates
> a rise above normal level and decay back to a normal
> If your amp's tuning capacitor arced, there are a lot of
> causes, such as a load changing under voltage, etc, and if
> you're using afsk, it could be the audio output from the generator,
> but certainly not from a keying spike which would not be
> present under rtty conditions anyway.
> Give us some more info on what happened.
> 73 de KL7HF
> -----Original Message-----
> From: RICHARD ANDREN <firstname.lastname@example.org>
> To: email@example.com <firstname.lastname@example.org>
> Date: Friday, December 11, 1998 4:39 AM
> Subject: [TenTec] VI+ Key Up Spike
> >There was a discussion here a while back regarding the key up spike
> >produced from the Omni VI+. Here's a little background to my problem. I
> >have no fancy test equipment, just a basic scope, meter, etc, so I can't
> >measure this stuff. I'm thinking about this now as I blew the main
> >cap in my MLA-2500 in the last rtty contest. Bringing the input to the
> >up slowly while keyed down or with ssb, no problem. I attempted to run
> >rtty contest at 700w output, well below what the amp can handle, but
> >1-1/2 hours, the main tuning cap melted, not a good thing! Could the key
> >up spike, or whatever you choose to call it, contributed to the
> >The MLA will keydown at 1000w, but maybe this spike that's been talked
> >about could have contributed? I agree the MLA design isn't exactly what
> >would call a beefy/built up unit, but this is what I've got to work with.
> >This was the first rtty contest I've used the amp for.
> >At this time, I can limp the MLA up to 1500w, but if I key it with a
> >juice, like 400w out, ZZZAP!!! I think a key up spike is initiating the
> >breakdown. Am I wrong?
> >I haven't fixed the amp yet because I may need to modify it with a vacuum
> >cap instead of the air variable. Maybe it has nothing to do with the
> >and it was just time for the cap to blow? I won't be able to read
> >responses until Monday morning. What do you think?
> >Hope to catch everyone in the contest this weekend on 10m!
> >73, Rick N9THC
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