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Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
I build this VTTC using 6146B and what I can find in my junkbox.currently no breakout but fluorscent lamps lignt up. Still don't know much about VTTC and don't know what adjustments I can do.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
hsieh, In reply to your questions: Try to find a cap with the 3-4 nF value, can be polypropylene film rated at least at 2000 volts, or you can make a mmc out of smaller ones. You can measure the resonant frequency by feeding the secondary base from a (grounded) frequency generator, through a 1k resistor. Scope the voltage at the base while changing the frequency. The frequency at which the voltage at the base is the lowest, is your resonant frequency. JavaTC is usually pretty accurate with these calculations. You can make a CT out of a toridal core from a common mode choke (from PC PSU, other SMPS etc), wind some 50 turns on it and shunt with a 10 ohm resistor.
So please post more details about your coil - secondary resonant frequency, primary form diameter, and I'll tell you how you can go about tuning your coil.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
I use larger capacitor on my voltage doubler(68u,the largest i can find) My primary LC resonant frequency is 620KHz,my secondary is 640KHz. primary:12cm diameter 9turns.feedback 12cm diameter 10turns tank capacitor is three 0.01u 630V audio grade MKP capacitor wired in serial. Rg2 now changed to 50K.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
From my calculations, with a 3 nF tank capacitor, you should use around 15 turns on the primary (wound over the length of 3 cm) with the taps on the last 7 or so turns. If you can't get enough power out of the coil, try a 4 nF tank cap and retune. Start with the outermost turn and decrease turns until you get good output.
The grid coil should have around 15 turns.
For the tank cap you should use a standard MKP or FKP cap, I have no idea if "audio grade" caps will work.
Rg2 should be in the 4.7 to 10k range in your case. Larger resistor = smaller output.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
hsieh, The primary circuit must oscillate below secondary resonance for optimal performance. If your unloaded secondary resonance is 620 kHz, I expect the primary tank to oscillate at ~450 kHz for best performance. (This depends on coupling and other factors)
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small 6146B vacuum tube tesla coil
