Re: SSTC problems1 (no its not a PlasmaSonic ;-))

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

Original poster: sebastian gaeta <sgtporky-at-prodigy-dot-net> 

These things are really a lot of fun, but they are a pain in the neck! That 
is why I called mine "The Beast". It is a wimp, and only produces 8" 
streamers because too much power is being dissapated in my MOSFETS, and not 
enough in the streamers! I just lit it up for the first time a few days 
ago, so all of your problems are still fresh in my mind :-)

I see that you have a scope, that's a very good thing and required for this 
work. The problem of the oscillation dropping out is due to the fact that 
you removed the 555. You need to put it back in and do some more tweeking. 
The whole purpose of that 555 is to start the oscillations, and keep it 
going when the line crosses 0. Find out what the resonant frequency of 
secondary system is, and adjust R4 (The 20K frequency pot) to that value. 
If you don't have a freq. counter remember that time is 1/frequency. Use 
the scope Luke, uh , I mean Jim! :-).

When you first start working with these things, you need really pure DC so 
that you can see what in the world is going on. You can switch back to 
pulsating later on after you get yourself straightened out. OK, now adjust 
R5 (The 100K in series with the output of the 555) to the absolute minimum. 
Don't apply power to the H bridge yet. Look at the gates of the mosfets, 
and decrease R5 until you see very narrow 15 volt or so spikes on them, and 
don't go any further. This should be the proper setting to kick it into 
working. It should look like this: 
<http://community.webshots-dot-com/photo/113763981/114110189mhjnYO>http://community.webshots-dot-com/photo/113763981/114110189mhjnYO 
Remove the probe from the gate. Never power the H bridge with a probe on 
the gates of the fets. This could add extra capacitance, and blow the fets. 
It may not matter with fets with a high gate capacitance, but don't risk it.

Now the scope comes into the picture once again. With the scope located 
about 5' away from your set up, place a short antenna pick up on it. Those 
rubber ducky scanner antennas with the BNC connectors work great for this 
stuff! Slowly increase the voltage on your H brige and watch the scope. 
Somewhere around 5 volts, the input current will jump up, and there should 
be a huge clean sine wave on the scope. If the primary is backwards, the 
sine wave will jitter around quite a bit, and the signal won't be anywhere 
near as large as it should be. The frequency will be wrong. Mine was 
oscillating at the second harmonic when the primary was backwards. I was 
also able to draw thick arcs from the coil, so your light bulb method will 
not tell you that the primary was wrong!

Good luck,
Sue

Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Jim Mitchell"

Hi Jan, et al.

Well I brought the antenna closer, and I touched my variac with one hand,
and the antenna with the other, heard that 60hz hum again, and I let go.
When I let go, I saw a squiggle show up on the scope, and the neon bulb on
top of the breakout point was lighting. I raised the voltage to 150, and
touched the neon bulb with a screwdrive, it got brigher then went out. I
tapped on the antenna again whilst touching my variac, and the oscillations
started again. I tried reversing the primary, same thing. What in the
world is causing this? It seems to be running off its own feedback but
power is like 000000 it is probably putting out 200v max on the breakout
point, and yes the secondary is grounded.

Regards - Jim Mitchell
----- Original Message -----
From: ! "Tesla list"
To:
Sent: Tuesday, January 27, 2004 9:54 AM
Subject: Re: SSTC problems1 (no its not a PlasmaSonic ;-))


 > Original poster: Jan Wagner
 >
 >
 > On Mon, 26 Jan 2004, Tesla list wrote:
 > > Original poster: "Jim Mitchell"
 > >
 > > I have ruled the problem out to be in the section that receives
feedback
 > > from the coil. The reason the coil is running crappy is because the
555
 > > timer is running it, instead of the feedback. It seems the feedback
doesn't
 > > have enough "oomph" to kcik in and take over the 555. So I removed the
555
 > > and banged on the antenna with a screwdriver. Neon bulb on the
breakout
 > > point flickered and I hear a 60hz hum in the GDT section, and thats it.
I
 > > will try more filtering on the input and see if I can get it to run!
with out
 > > the 555.
 >
 > If you've a filter after the feedback antenna, don't! Filters just
 > attenuate or screw up the phase. (on the mains voltage side, a larger
 > smoothing cap is of course fine, but streamers will start looking
 > different)
 >
 > Placement of the antenna is often surprisingly critical. You can try using
 > different lengths of wire (~20..40cm) and lying it out in different ways
 > e.g. on the desk/floor: towards coil, counterclockwise along coil,
 > clockwise, ... Or sticking up vertically, etc.
 >
 > good luck,
 > - Jan
 >
 > --
 > ****************************************************
 > Helsinki University of Technology
 > Dept. of Electrical and Communications Engineering
 > http://www.hut.fi/~jwagner/ - jwagner-at-cc.hut.fi
 >
 >