Tesla List wrote:
> Original Poster: VGREAT-at-aol-dot-com
> WOW AM I CONFUSED NOW.  We have a small coil 5"x22 powered by a 15kv 60ma
> NST.  using 0.012uf cap.  Our current spark gap is 18 sections of cu pipe
> with a total gap of 0.300"  this gives us nice 4 foots streamers off a 16"
> corona ball.  Well we never are satisfied with what we have so had to try
> something new.  replaced the spark gap with a hydrogen thyratron, thinking it
> would be quieter and improve the Q so all would be better.  Well .... the
> thyratron would not hold off the voltage as expected and freely anode fired
> without any trigger applied. Used a thyratron rated for 16kv and only had
> input powerstat at about 3kv.   but that is not the question.. the question
> is why did the coil get big arcs up and down the secondary while the tube was
> anode firing?????
> any ideas would be greatly accepted..
> Phred and Inspector Mike

I suspect the initial breakdown voltage of the thyratron may be higher
than that of your sparkgaps, so the initial "bang" energy may now
higher, and the peak output voltage on the secondary may be higher as
well, overvolting the coil. BTW, using a thyratron as a triggered
spark-gap may result in a lower Q since the fully conducting "on"
resistance of the thyratron is normally higher than that of a series of
sparkgaps in air. However, the "on" voltage drop for the single thyraton
may be lower than for the series of gaps since you'll only be seeing a
single anode and cathode voltage drop in the thyratron. Thyratrons
should normally only conduct in one direction to prevent damage to the
cathode - if your system is self-triggering, your may also be exceeding
the reverse PIV. Since your tank cap is set to resonate with your NST,
you may actually be seeing voltages MUCH higher than 1.14 X 15 kV by the
time the thyratron breaks down. If you were using a 5C22, for example,
you were substantially overvolting it. What type thyratron were you
using, and what type trigger source?

-- Bert --