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Re: VTTC question

Original poster: "Dr. John W. Gudenas" <comsciprof@xxxxxxxxxxxxx>

Matt
I have found differences between tubes in my VTTC's but none that
severe.

Can the "new tube" be at the end of its life? Certainly. There are,
other possibilities.

Apparently that tube is a Russian import with a carbonized thoriated
tungsten heated cathode.
It is possible the electron emission is low from the cathode or that
the screens got damaged in shipping.
With a pentode there is ample opportunity for the three grids to get
damaged.

Another possibility is the tube got somewhat gassy. Try letting it
run with just the heater on for a few days.
I don't know if it needs air cooling for prolonged runs, but if it
does, supply the cooling.

You are sort of at the mercy of Russian military surplus.
Good luck.

John W. Gudenas, Ph.D.
Professor of Computer Science

On Jul 13, 2005, at 7:18 PM, Tesla list wrote:

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