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Yes - the 4.4k is the bleeding resistor of the grid feedback circuit.
In my coil - the second grid is coneected to +1kV trough a bunch of resistors. This way the tube works as a triode. I've used grid 2 to do modulation on the coil and to connected a staccato. It worked perfectly.
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
Conecting the grids together would work? I never used tetrodes before.
If not, I will feed the grid 2 through a variac-MOT rectified.
At nominal plate voltage (33 kV for GMI-90) Ug2 = 1750 V. At 10 kV plate voltage the grid 2 voltage would be 583, around 600 V. At 45 W dissipation it means a current of 75 mA, so i need a 8000 ohm resistor @ 45 W. I dont have high power resistor, but a 25 W light bulb has a underload resistence of 1936 ohms, so I can use 5 x 25 W light bulbs as a 9680 ohms @ 125 W grid 2 resistor.
(NB: Ups, I think I am wrong because U = I*R + Ug2, so for U = 1000 V, and Imax = P dissipated /Ug2 = 75 mA, I would have a 5333 ohms G2 resistor. Sorry)
I dont think that I have the possibility to modulate the grid 2. Can be used the cathode modulation through a pulsed IGBT?
Impulse voltage on grid 1 is around 300 V (almost similar as for GMI7-350 V), but on shorter duration (3 microsec vs 5 microsec). But for 1/3 Va I can consider a 10 microsec pulse with no big problems. So a 4-5 kohms grid 1 resistor would be ok.
Has someone some spare SANGANO capacitors ( as used in Quadzilla)?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
nice work Dr. H. do you plan up the F res to get the sward sparks?
Is the efficiency differant because the tube is a pulse tube? in moast armstrong VTTC's the tube is on only for a half cycle or less I would think that a pules tube would work better for that setup. because it is not a linear tube could G1 be pulsed trigger VS a linear input if so the fireing angle and power could be controled with a staccato pulse.
Do pulse type tubes have a faster recovery time than a thyrarton whats the diferance?
Registered Member #3974
Joined: Mon Jun 27 2011, 06:50PM
Location: Germany
Posts: 23
what scematic did you use for it? standerd class-C triode armstrong oszillator, G2 conected to G1, or G2 on a HV powersuply? or a new kind of VTTC Scem? could you send me the scem cuz i wana learn from it.
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4Kva Dual GMI-7 VTTC - FIRST SPARKS
