Re: Ross-O's VTTC update

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

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

In a message dated 1/22/01 10:13:36 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

> (2) I played around a bit with calculating the sideband freqs and then
>  measuring them by looking at the resonant freq of the primary with the
>  secondary in place.  The measured upper freq didn't match my calculations.
>  Any ideas?  Forgive the lack of details in this post.  I'm keeping 
bandwidth
>  low by putting all the details on the web page.

Ross,

When I used a spectrum analyzer to observe the actual operating 
frequencies in an operating VTTC coil, the primary frequency
seemed to be shifted downward about twice as much as bandwidth/
freq splitting calcs would suggest.  I'm not sure why this was, but
the coil ran the best that way.

When I tune my coils I first aim for max spark length.  Next,
I made smaller tuning adjustments to find a tune point which
maintains the spark length, but gives cooler tube operation.
I noticed a tuning range, over which the same spark length is
produced, but tube runs cooler near the edge (s ?) of this range.

Could it be that your grid coupling is much too low?  The distance
between the primary and grid coil is as important as the number of 
turns.  You may be compensating for low grid drive, by using a
small negative bias.  This will make the tube conduct for a wide
time-on angle, but with weak conduction when it conducts.  You
want a high bias, with very strong grid feedback pulses for good
efficiency.  But not too strong.... you don't want the grid to become
more positive than the plate.... or the grid will act like the plate,
which is "bad".  This will probably cause a raspy sound if it
occurs.... and may be caused by too much grid drive.  Just
thowing out some ideas here.

I didn't re-check your site yet, so when I do I may have something
else to add.  In any case, your results are very interesting.

John Freau