Re: Building a 3-1000z VTTC

In a message dated 99-09-01 20:55:05 EDT, you write:

> 1.  What is the largest diameter secondary that this tube can power?


Nice find!!    I once used a 3-500Z in a tube coil. It gave about a 17" spark.
I assume that the 3-1000Z can give a 24" spark.  Probably more, because
I was learning when I built that first tube coil.  I don't know what the limit
for the secondary size is, but I sucessfully powered up a secondary that
was 7" dia, by 30" high with a similar amount of power as a 3-500Z can
handle.  My coil schematic at David Trimmell's website that uses (3)
833A's should work well with one 3-1000Z.  The grid-leak resistor, and 
grid feedback coil position will probably need to be adjusted for best
results.  The primary might need more turns, along with a smaller cap
for the best impedance match.  I'll have to check my notes for when I
did run the coil one using (1) 833A one time for a 22" spark.

> 3.  The tube specs state the the filament needs 7.5V at 21.3A.  The
> filament transformer that came in the box is a 7.5V, 25A.  Is this OK or
> do I need to drop the current somehow (add series resistance?)

My guess is it will be OK.  You can measure the voltage on the filament
with the tube filament powered up, if the voltage is not more than 5%
high, it should be OK.  If you need to drop the voltage, you can use
wires from the filament transformer that are a little bit thiner and/or
longer than normal. They'll run slightly warm (the wires), and drop the

John Freau
> Thanks,
> Ross Overstreet >>