Re: VTTC Questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>


Andy,

0.85uF is probably too large for a bypass capacitor, because
it will tend to bypass the 60Hz AC also.  The bypass cap value
is not critical, but should be in the range of 0.001uF to 0.01uF or so.
Fixing this issue may give you a big improvement in performance.
(I just looked at David T's schematic, and I see that he shows
a 0.85uF cap.  I can't explain that, because I didn't think it would
work well.  Maybe he changed it and forgot to show it on the
schematic.  I don't know.   In any case, I'd try using a smaller
value there.)  If it doesn't help, (and if the tube is capable of
getting red (the plate)), then I don't know why you're
getting only 1" of spark.  I assume you connected the both
tube grids together; screen and control grids.

Oh, something you can try if you haven't is to reverse the
grid coil wires.  It may be 180 degrees out of phase.  This
will kill a coil's performance like nothing else until it's corrected.

All the other values look good to me (without doing any calcs).

It may be best to tap the primary at the bottom rather than the
top, because tapping may affect the voltage induced into the grid
coil.  Any changes in the primary tap point will change the
grid feedback.  If you can adjust the spacing between the
grid coil and primary, you may be able to compensate to some
degree.

Tapping the primary will change the tank impedance, and
if you use too few primary turns, the tube may get too red.
I'd think you'd want to use at least 23 primary turns at all
times for this reason.

In general, more grid leak resistance will make the tube
run cooler and the spark will shorten some.  It doesn't always
work this way depending on other adjustments.  Grid
leak capacitance won't make much difference within
a wide range.  The values you used are fine.

Wintesla should be fine for a tube coil for basic tuning calcs.

Primary secondary coupling is critical on some tube coils,
much less so on others.  It depends on all the other parameters.
Usually it's not too critical.

Height of topload makes little difference, except perhaps
as a tuning aid.

If the tubes plates are capable of getting bright red, then they
have good emission.  Sort of an orange-red actually.  It's unlikely
both tubes would have the same type of flaw.  

Tube coil tuning and adjustment is critical for best results.
The various adjustments tend to interact, so it's tricky and
takes time to get it all right.  It's easier if you use meters
though.

John