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Re: VTTC question

Original poster: "Mike" <induction@xxxxxxxxxxx>

Hi Matt,
I would not expect the spec to be that great one tube to another as far as running the TC out of tune. Maybe you can bias the tube on in a DC test and see if it will pass the same current as your existing tube. Run it in the diode mode; There will be no RF output and all the power will be heat so cool it well beyond normal. I don't know if you are running that tube triode connected but maybe the prior owner did something stupid like running screen without plate voltage and fried he screen or the signal grid. Like you say, maybe it is really used and soft as a melon. You need to see how much current it will pass as a diode, could be the filament has low emission, the diode test will tell you this.
In that power class I would have chose maybe a 3-500Z (with a lot of drive) or if you wanted a tetrode a 4-400A, at least those are common and available. Of course you may have got a real good deal on the tube you are using. Anyway, that is one test.
Mike

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, July 13, 2005 8:18 PM
Subject: VTTC question


Original poster: "Matt Whitman" <teslacoiler@xxxxxxxxxxx>

Hi all,

I have a VTTC in which I am using a GU-81M pentode. I figured since I only
have one I should get a backup tube just in case. So I found another GU-81M
on ebay and it was supposidly new, so I bought it. Tonight when I went to
try it out on the coil there is no breakout and a very little spark when I
touch a screwdriver to it. My question is: could the tube have slightly
different ratings so that tuning the coil would correct the problem or is my
new tube actually used and at the end of its life?


Matt Whitman
teslacoiler@xxxxxxxxxxx
http://web.a-znet.com/~teslacoiler/index.html
KC2IEV