SSTC

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Original poster: "Chris Swinson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <exxos-at-cps-games.co.uk>

Hi all,

I've managed to build up richie's SSTC though its working I've been testing
a few coils out and have a few questions to put to the list to see if anyone
can relate to them. The first thing I noticed was my older 212khz coils
wound with 0.8mm wire dont seem to work at all with the SSTC. I used these
coils with 250watt spark gap type coil and got good results from them. The
SSTC is about 200watt so I would have thought they would work just as good
or even better with the SSTC than the spark gap coil. From what I can tell
the SSTC should be more effieient so I would assume it would give longer
arcs ?

With the 0.8mm wound coil I am not sure but I am having problems tuning the
coil. I added a small jumper resistor onto my circuit so I can sweep down
the frequency range a bit more. Though with my 0.8mm wound coil When I turn
up the frequency I seem to find many tune points. It starts off very low
power first of all. I am using a small 12" flo-tube to monitor power levels.
As I keep turning up the tube goes out, then comes back on again a little
brighter, then goes off again, then comes on a bit brighter...etc etc.. Then
I reach the end of the 22K tuning pot and I turn it down to 0 and add in a
fixed 22K resistor so I can start off with the frequency I left off at...
Though in doing this I can't find any tune points at all. I know the circuit
is running since I've had it on my scope and checked it all out.

My test coil was wound with 0.4mm wire. this one worked a lot better. The
same "in and out" of tuning effect occurs. Though it gets brigther and
brighter, then fades back off again, where as my 0.8mm coil didn't. It seems
very much like the 0.8mm coil isn't running at all when I add in a extra 22k
resistor in there, though it works on my scope fine... I also tried a 0.2mm
wire coil and this one worked the best.  Now im not 100% sure what frequency
the 0.2mm coil was though I think its about 300khz, my 0.4mm coil was
350khz, my 0.8 coil 212khz.  With all my normal spark gap tests the thicker
wire gave a little better spark length then the smaller wire. I found 0.4mm
to probably be the best. Though why does 0.2mm work better with a SSTC ?

I looked into couping since everytime the wire dia goes up so does the
height of the coil. I can only imagine that more power is being transfered
with the smaller dia wire than the 0.4 or 0.8mm coils. I did wind a primary
out of a lot thicker wire and try it on all 3 coils though there was nothing
I could see to be of any benefit.  The only way to try this is to wind a
coil with very large dia wire such as 1" wide cable and see if I can get the
power up on the 0.8mm coil. I have seen a SSTC somewhere else on the
internet and thier primary and secondary was about the same as mine in size
relationship and they got good results. I'm not sure what poer input was for
theirs though. Does anyone know how crytical the coupling is for a SSTC ?

One thing which I must does is make better insulation from primary to
secondary since the 0.2mm coil glows purple around the primary and I think
this could have blown the output stage of my SSTC since the primary was
probably been spiked from the power. I'm thinking of adding on the output a
lot of 600V voltage suppressors in case it happens again. What I was
thinking is winding the primary inside the secondary. I thought about this
since finding a smaller form to wind the primary on is a lot easier than
finding a biger one. since the secondary form is 5mm thick it would give
some good insulation to the primary. I can also easily find a tube say 1inch
smaller in dia to give a good air gap between both tubes. I dont see any
problems in doing a inside primary ?

Thinking about it a little more , in some spark gap coil tests I did last
year , I tried a simple magnifier setup. Didn't improve much really in
anycase.. Though with this setup the secondary is base-fed from a smaller
100turn driver coil. the driver coil being close coupled to the primary. I
would imagine this would be a safer method for the SSTC since no high
voltages would be close to the primary. Base feeding the secondary means I
can keep it well away from primary. Has anyone tried this ? I would imagine
everything with the SSTC will be the same for a VTTC also, so if anyone has
any thoughts on this then please let me know.

thanks for tuning in :)
Chris