SSTC first light, 6" -at- 120VAC

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

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hello All.

It's nice to be back on the list again after a couple
weeks of not having it, due to some PC/internet/email
changes of mine!!!

My email has changed to pyrotrons2000-at-yahoo-dot-com

NEW PIC'S AND INFO of our current SSTC work: 

www.hvguy-dot-com

Just below the disclaimer, in yellow font, it says
"Recent SSTC developments" or something close to it.
Click on the blue link.

The arc pic's didn't turn out well, but everything
else came out great, especially the WAVEFORMS (cool!).


Aron and I fired my SSTC for the first time last
weekend, we had decent results -at- 6" sparks with
half-wave rectified 120V input. 

Unfortunately, we couldn't run at full rated input
voltage (350V peak or so) because the circuit was
eating FET's and the superfast diodes that protect
them (think there could maybe possibly be a
correlation here somewhere??!!). 

The superfast diodes are SF56's from Mouser, rated
50nS 5A 400V. A little low on the voltage, I would
prefer no less than 600V or so, maybe 1kV for
bullet-proof-ness. (I know Motorola makes 30nS 5A 1kV
jobs! MR54's I think?? Aron pulled one out of a TV
when we ran out of our original diodes) The MOSFET's
are IRFP460's that Aron had on hand, they're rated
500V 28A in a TO-247 package!! It's really sad when
one of them dies ; (

Anyhow after a few mod's we expect strikes out to 21"
max when run with 240V full-wave rectified AC into the
MOSFET's. That extra input voltage overcomes the FET's
"ON" resistance, and performance goes up significantly
from there.

The overall design is based on Richie Burnett's SSTC
(www.richieburnett.co.uk), although Aron and I have
heavily modified it in ways. For those who don't know:
there are two main circuits: the "control" electronics
and the "H-bridge". The control electronics are based
around a TL494 (NTE1729) PWM chip, the squarewave
output of which drives some common NPN and PNP
bipolars (2N3055's for NPN and TIP42's for PNP is what
I used......Richie is using ZTX450's and
ZTX550's....they both work great....). The output of
the bipolars is what drives the gate of 4 heavy-duty
MOSFET's arranged in an H-bridge configuration. A
wonderful way to do things, I would shake Richie's
hand for that one.

Something neat I noticed last night: I installed some
RF bypass capacitors on the board when I made it, I
figured they couldn't hurt for VHF
oscillations/ringdowns/etc. that weren't supposed to
be there. SO FAR, the circuit has been fairly
predictable. When I had it running last night, I took
out the bypass cap's to see if they were doing
anything at all.

One of the FET's and one of the superfast diodes died
violently, so I now know that the cap's are doing
something other than taking up space on the board.

A massive thanks to my best bud Aron for sacrificing
his FET's to the SSTC God!!!!! I know I couldn't have
got this working as quickly as I did without him. 

Also, thanks to Richie Burnett (although I don't think
he is on this list) for the original design, it is a
good one. 

Hope you all like the pic's and info.....let us know
if you did or didn't, Q's, comments, whatever.
pyrotrons2000-at-yahoo-dot-com

Take care,

Justin Hays
KC5PNP
Email: pyrotrons2000-at-yahoo-dot-com
Website: www.hvguy-dot-com















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