RE: ISSTC questions - Half-Bridges

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

Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com> 

Yes I believe tune is the key point (at least one of many!). Last night
I did some testing (my wife and daughter were out of town...), and now I
get reliable get 22" sparks to an ungrounded Ring Stand on a shelf. But
I wondered just how far anyone has pushed a Half-Bridge? So far I am
vary happy with my results, I mean I am getting 22" sparks at ~0.8KVA!
Try that with a vacuum tube!? Another note I would like to say; while I
am using a protoboard and not providing any RF shielding to it (only
4-5" away from primary on a table, same plane) it must be earth
grounded. I tried "floating" the ground and everything was great until I
upgraded to my 6" secondary (due to greater RF interference), then it
became very unstable. Once I grounded the negative, things are vary
stable now. But I must note on just how hot the primary can get. When
the sparks are flying, I must watch the primary tank, as it can get very
hot. So far I have kept run times to less than one minute without
breaks. BUT, the IGBTs stay rock cold with a fan running over the heat
sink! I think that I could upgrade my primary to copper tubing and
increase the current capacity of the tank cap, and then this sucker
could run for extended runs. The museum TC folks may want to look into
this...

But again what have people done spark wise with a half-bridge?

Regards,

David Trimmell


-----Original Message-----
To: tesla-at-pupman-dot-com
Subject: Re: ISSTC questions

Original poster: "Eastern Voltage Research Corporation"
<dhmccauley-at-easternvoltageresearch-dot-com>

It sounds like you may have just not found the optimal tuning point for
your
coil.
You need to tune the ISSTC just as you would a spark gap coil.