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Re: Really big VTTCs

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 06:07 PM 1/24/2007, Tesla list wrote:
Original poster: Shad <shenderson@xxxxxxxxxxxxxxxx>

Hi All,

It's very important to keep in mind that if you triode connect a pentode
(tie the screen to the plate), the maximum voltage of the *SCREEN*
becomes the maximum plate voltage.  You'd be better off building a
dedicated screen supply (or using a dropping resistor) to supply power
to the screen.  Sure, it'll burn off power, and complicate things a
*little* bit, but it's much better than really limiting the plate
voltages you can run.

Also, don't exceed the dissipation rating of the screen.  They have a
specific job to do, but they lack the anode's ability to shed heat

Tetrodes are the same way.  When the second grid is connected to the
plate, the maximum plate voltage drops.  It's much easier just to use a
suitable dropping resistor to feed the extra element.

Just figure the voltage drop and current necessary for the screen and
then calculate the appropriate resistor for it.

Anyone contemplating this sort of thing should get a copy of Eimac's Care and Feeding of Power Grid Tubes. It's on CPI's website

You might try

Heed all those warnings..

The LANL High Power Microwave Transmitter report by North also has useful information, but the care and feeding book is probably a better source for circuit design.

Hope it helps!

Shad H.

> I've read that the tetrodes are a little less convenient, but still
> usable by connecting the grids: