Re: [TCML] Negative bias in a VTTC

[DC Cox <resonance@xxxxxxxxxxxx>]

I sspect these red hot condition is NOT caused by the bias.  It's being
caused by parasitic oscillations which produce similar effects.
See the 1984-86 edition of the Radio Amateur's Hankbook for the cure.

D.C. Cox


On Wed, Sep 22, 2010 at 11:29 AM, James <mustang3@xxxxxxx> wrote:

> Hi Vladi, I urge you to view my VTTC on youtube (big VTTC). I posted some
> video of it running, along with o'scope pictures and Spectrum Analyzer
> pictures. You have got to hit the tube's grid hard enough to completely
> turn
> it off. On a low mu power triode, this generally takes several thousand
> volts negative. Low mu tubes are generally better for Tesla coils. You also
> need to have enough primary turns to properly load the tube. Too few turns
> causes the tube to run hot. Around 25-30 turns of primary is a good start.
> Then match the primary capacitor. The tickler winding needs to be a few
> turns less. The grid leak resistor controls the current through the tube.
> Monitor the cathode current and set accordingly. James
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Vladimiro Mazzilli
> Sent: Wednesday, September 22, 2010 10:44 AM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] Negative bias in a VTTC
>
> Hi all.
> A friend of mine have problem with  grid leak network of a single 833 VTTC.
> He started with a 5k resistor and have increased its value reaching over
> 25k, but with a MOT without doubler, he has always the plate very red.
> I noted that triodes have different plate current value with 0V biased grid
> independently from the power of the tube: 811A is very simple to bias at 0V
> because the plate at 2000V reach only 20mA of plate current from the
> curves,
> otherwise 833 drain 500mA from plate, with grid  biased at 0V and with
> 2000V
> on plate.
>
> Had anyone made test with grid leak resistor connected at a variable dc or
> 'in phase' ac and grid leak capacitor grounded?
>
> Cheers
>
> Vladi
>
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