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Re: Sword-like VTTC spark pix (ceramic tube questions)

Original poster: "brian by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ka1bbg1-at-mcttelecom-dot-com>

Hi, parasitics will cause excess plate current and that overloading can kill
a tube real quick especially if its a ceramic vhf tube. most of the older
glass tubes were low frequency so less likely to have parasitics. I built an
rf amp for 1kw on ham bands with 4 4cx250's and ended up killing the first
batch of 4. (oouch) there was a post a week ago or two and the author had
made numerous amplifiers for hf ham band. there was a whole bunch of stuff
on his site about tubes and amplifier. his work is found in the ARRL
handbook. will try to find his site for you...cul brian
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, February 10, 2001 12:48 AM
Subject: Re: Sword-like VTTC spark pix (ceramic tube questions)

> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> Hey Brian,
> Good point about the downsides of these ceramic tubes.  I was under the
> impression, though, that their electrode structures permitted them to be
> conditioned for very high voltage use.  The 833-A, my favorite glass tube
> for economy and power, can only (ha!) be used up to 6 kV or so, but I
> recall hearing that some of the ceramics can undergo a special burn-in
> procedure that dramatically increases their flashover ratings.  (Does it
> have to do with a cylindrical electrode structure?)  This would make them
> especially suited to VT Tesla coils, which from my experience and I think
> that of others, do best with a high plate voltage and high L to C tank
> ratio.  Do you know if the ceramics have any particular tendency to have
> strong parasitics over glass tubes?  I've never used VHF suppressors on
> tube coils, but then these tubes (like 833-A) have much lower gain at VHF
> than most ceramics.  Thanks for the comments.
> Carl
> >Hi, the only advice for ceramic tubes -vrs- glass is 2 things: 1 use the
> >correct tube base with cooling,2 start out at low power until you are
> >there are no parasitics and tuned up. ceramic are hi-power for their size
> >but without good tuning and the right amount of air cooling they go PUFF
> >real easy. cul brian