Re: 304tl experiments...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Brett Miller <brmtesla2@xxxxxxxxx>


> Brett,
>
> By interrupter do you mean the staccato control
> timing
> signal controlling the SCR?  I might not be
> understanding
> exactly what you're suggesting.

Well, I was brainstorming the other day about just
trying to adapt my simple SSTC interrupter for use
with a VTTC.  All it consists of is just a 555
oscillator with one pot to control PRF and another to
control on time (the one Steve Ward shows on his
site).  I use a shielded metal box with an RCA to
allow me to change the bps and pulse width remotely.
Without the interrupter, (because of the full bridge
and big filter cap on my 30v transformer) the sparks
on my SSTC are CW and have the classic flame and hiss.
 With the interrupter running at a PRF of 60 and the
on time about mid range, my sparks look a lot like
vttc sparks.  With a faster PRF and low on time, the
sparks look more like a disruptive coil.

I realize you designed your staccato (the one which
Steve also uses) circuit to run efficiently due to its
zero crossing detection capabilities.  Because of this
it will not trigger the vttc system at arbitrary
points in the mains cycle.  My main question was,
wouldn't this zero crossing circuit be uneeded if I
were to staccato pulse a vttc which was running off of
rectified and filtered MOT output since the filter cap
would allow the circuit to deliver a constant energy
regardless of when the staccato pulse occured?

Then I would simply need to find an SCR (or IGBT?)
which would switch fast enough, and would run with
simple enough driver circuitry to prevent the idea
from being an excercise in redundancy.

I guess I just thought it would be neat if I could use
the same remote interrupter box for my SSTCs and my
VTTCs.  Hmmm, maybe Steve Conner's Brick driver
circuit might work for this.  Again, this might be a
waste of time (and an IGBT) unless it can allow me to
do things with a vttc that I couldn't do with your
circuit.



-Brett



>
> An SCR requires the removal of the positive voltage
> (for
> a sufficient time duration) before the SCR can turn
> off.
> A different device other than an SCR would need to
> be
> used unless an SCR is available which can turn off
> within one RF cycle.  When I did my duty cycle
> control experiments (which required shutting off the
> oscillation during positive plate voltage times), I
> used
> grid controlled staccato and supplied a sufficiently
> negative voltage to the grid to cut off oscillation
> despite
> the oscillator "wanting" to keep running.  This
> strong
> negative grid voltage could possibly destroy the
> tube I think.
>
> An interupter such as a mechanical rotary switch
> could
> be put in series with the SCR anode, but then the
> SCR wouldn't
> be needed.
>
> A hydrogen thyratron should work in place of an SCR,
> but
> there may be some suitable solid state devices
> available in
> today's world, which can handle the voltage and
> current,
> and turn off fast enough.
>
> John
>
>
>
>
>
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>





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