Re: [TCML] 833A VTTC schematics

[bturner@xxxxxxxx]

Looks like a half-wave plate voltage doubler, and each 833 has it's own
plate load 'equalizer' network. The only real snaffu I can see is that the
cathodes (filaments) are not being run 'balanced'. The best thing is to
use (a) center-tapped cathode transformer(s) and either ground the center
tap or modulate it at that point. (You can also get a reading of plate
current by placing an ammeter in series...) This keeps cathode current
flowing evenly down each leg of the tungsten preventing one side from
getting 'hotter' (electron emission-wise) than the other which helps
prevent cathode destruction. Also, I've heard that cathode voltage is VERY
important. Too low, and you get electron migration out of the tungsten
which shortens the tube's life. Run them too hot, and cathode emission
goes up, driving plate current up, again, ultimately shortening tube life.

Also, don't let the tubes bang physically against anything - the cathodes
are somewhat brittle, and can easily shatter under a surprisingly low
impact force. 833's use a ribbon cathode if memory serves, but still,
pamper them...

- b

I have used the balanced cathode current arrangement in my VTTC which runs
two 805 triodes in parallel, 1200V raw AC to the plates (self-rectifying
oscillator) and the coil is now over 12 years old and still runs with a
strong and hot 6" discharge. I have yet to re-adjust the grid current.
(Though I am driving the tubes a bit conservatively, as replacements
aren't cheap anymore.)



> I have acquired (2) 833As. I have looked at several VTTC schematics, I
> am leaning towards Dans
> http://www.easternvoltageresearch.com/resources/vttc833a_fullschematic.pdf
>              This will be my 4th coil, but my 1st VTTC. Any advice,
> suggestions, or warnings would be welcome.
>
> Thanks Wm A Tickhill  (aka Hairball)
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>


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