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Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
In The AC model values of Cgp and Cgk are affected by the operating voltages and the admittance , Y (1/Z) of the grid is the factor that allows calculation of the power in watts that the grid consumes, even though it never crosses over to positive drive.
Any valve amplifier has a signal input and output wattage. The generates noise across the G (1/R) portion of Y and noise is merrily added by the thermionic process.
Of interest is the paper written by the National Bureau of Standards just at the time valve makers were getting so good at what they did, the mathmaticians were called upon to measure it.
Registered Member #2958
Joined: Sat Jul 03 2010, 02:36AM
Location:
Posts: 8
I am reviving this because I have had no luck on developing a circuit to do this.
My goal is to use a 4000vdc supply feeding a GU-5B to drive the primary coil.
I need to be able to trigger the GU-5B from the output of a HP signal generator allowing me to experiment with different frequencies.
If the tube needs -100/+400 , is it possible to tie the grid through a resistor to -100v and then modulate the grid with a mosfet tied to a +400 supply
The HP would feed a pulse to a mosfet driver and the mosfet driver would drive the mosfet.
There must be someone here who knows how to do this, any help would be greatly appreciated
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
darkspeed wrote ...
I am reviving this because I have had no luck on developing a circuit to do this.
My goal is to use a 4000vdc supply feeding a GU-5B to drive the primary coil.
I need to be able to trigger the GU-5B from the output of a HP signal generator allowing me to experiment with different frequencies.
If the tube needs -100/+400 , is it possible to tie the grid through a resistor to -100v and then modulate the grid with a mosfet tied to a +400 supply
The HP would feed a pulse to a mosfet driver and the mosfet driver would drive the mosfet.
There must be someone here who knows how to do this, any help would be greatly appreciated
Yes, you can use a bridge for driving the grid. I have heard of a sort of hybrid tesla coil using mosfets to drive a tube. A schematic like this would work
EDIT: Not sure how the double post happened, it says each post was at different times.
Anyway, i forgot to say that the two inverters are just there to represent mosfet drivers, though you could of course use any kind of amplifier as long as it drives the mosfets with a squarewave.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Either ground the grid and use a 400V power FET to drive the cathode, or use another smaller tube to drive the grid through a coupling capacitor and bias resistor. I've seen the latter done successfully using an EL34, EL84, 6146 or similar to drive a GU81M that in turn powered a Tesla coil.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
No, I'm not sure who built it, might have been one of the guys on the TCBOUK mailing list years ago, but I can't remember a name.
I don't think he ever published a schematic. I just remember that he wanted to make a VTTC driven by an oscillator instead of the usual self-resonant kind, and contacted me looking for help.
He ended up with a "multivibrator" type oscillator made from a 12AX7, with its frequency controlled by a pot, driving some sort of power tube like an EL34, that was coupled to the grid of the GU81. Apparently he was quite happy with the output.
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Driving triode from signal generator
