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Re: 813 VTTC Problems
- To: tesla@xxxxxxxxxx
- Subject: Re: 813 VTTC Problems
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Mon, 29 Aug 2005 16:54:15 -0600
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- Delivered-to: tesla@pupman.com
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- Resent-date: Mon, 29 Aug 2005 16:57:39 -0600 (MDT)
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Original poster: Steve Conner <steve@xxxxxxxxxxxx>
How exactly should the G2 and G3 grids of these tubes be connected
to the circuit? And are they actually supposed to draw current?
G3 connects to the cathode. G2 (aka screen grid) connects to a
positive bias supply and can draw significant current. 4kV is far
more than should ever be applied to the screen- it's usually nearer
200-500V. Check the tube datasheet for suggested values of screen
supply voltage. dropper resistor, and to get an idea of how much
current the screen will draw in use.
Some tubes work OK as triodes with G1 and G2 connected together and
driven as a control grid. But G1 can draw a lot more current than G2
and overheat sometimes.
If the plate supply to a tube like this is halfwave rectified
pulsating DC (as some VTTC builders use) then the screen supply
should be halfwave rectified too. Otherwise the screen can overheat
since it draws excessive current when there is no plate voltage.
Steve Conner
http://www.scopeboy.com/tesla/