vttc(3-1000z)

["James" <mustang3-at-home-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ross an others,
   I am really jealous of that big toob. Those are hard to find. Some key
points you need to be aware of. You need about 20-25 turns of primary, got
to keep the impedance high for the tube. After you figure your secondary,
then plug in 20 turns for the primary and calculate the cap. I ran WinTesla
and I get 1 Nf for a 20 turn pri. ( -at-400KHz ) Wind the tickler (grid) coil
below the primary by 1/2 to 3/4 inch. You need enough drive to turn the tube
on and off smartly. I would start with 18 turns of small wire #18 or #20
maybe, and go up or down from there. The value of the grid leak resistor is
determined by the conductivity of the tube. 2K to 8K is normal. The grid
leak cap doesn't need to be too large .001 to .01 uf is ok. To reduce stress
on the filament, use a center-tapped transformer. A rewound MOT makes an
easy, cheap one.
	My vttc uses 2 833a's with John F.'s voltage doubler(level shifter)PSU, a 6
in. X 24 in. of #27 wire for the secondary. This runs at 165 KHz. 20 turns
of #8 for the primary, with a 6 Nf-at-8000 volts cap., 19 turns of #18 for the
tickler. 3.6K 75 W resistor, .02 uf cap for the grid leak. With 120 volts
input I'm getting 15 inch arcs and at 140 volts input, I'm getting 18 inch
sparks. The coil will light up a fluourescent lamp 6 or 7 feet away. The MOT
gets very hot and I have to limit run times. The coil works well. I had my
o'scope hooked up to it and saw some interesting things. Using my X1000
probe, I found pulses of +300 and -3000 volts on the grid. The anode had
positive pulses of 8000 volts. This may explain why the tubes get red hot so
quick. The +300 pulse on the grid turns the tube on. This makes a big pulse
in the primary coil. Then, since the feedback (tickler) winding is out of
phase, the negitive pulse generated turns the tube off. Now the PSU, is a
half wave voltage doubler, It only outputs every positive portion of the 60
cycle input (30 pulses/sec). So, the tube is only working for half the time.
If you run the coil on AC, you get the same result. Only you don't get the
voltage double action. My next modification is going to a full wave bridge
rectifier, with 2 MOTs (primarys in parallel, secondaries in series). This
will give MORE POWER.
	Well, I've gotten pretty wordy so I'll chill for now.
										Later,
										  James