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Re: VTTC capacitor



Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net>

I do not understand your comment about pulse caps handling only DC. Even
when used on a disruptive coil, every time the spark gap fires this closes
the circuit on the primary tank circuit. The tank rings with a damped
sinusoid (AC) each pulse. Thus, the pulse cap is subjected to AC. I happen
to have a 0.0015 uf pulse cap rated at 15 KV. This should be a very good
size for a tube coil. I am still seeking an answer to my question about
frequency applicability of a pulse cap. I suspect that it it should not be a
problem because most tube coils seem to operate at under 1 MHZ frequency.

Steve: Coiling in Iowa

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, February 11, 2002 4:46 PM
Subject: Re: VTTC capacitor


> Original poster: "Area31 Research Facility by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rwstephens-at-hurontario-dot-net>
>
> Steve,
>
> Tetrodes are poor choices for self excited RF power oscillators.  This
tubes
> triode counterpart, a 3-1000 would be an excellent tube.  All commercial
> industrial RF induction heating systems that use tubes employ triodes for
a
> good reason.
>
> Pulse capacitors are usually designed for so many 'shots' or discharge
cycles
> with minimum percentage voltage reversal to none at all.  For this reason
I
> would have to recommend not using them in a CW RF tank circuit where 100%
> reversal at the RF frequency is the norm.
>
> Relatively large values of tank cap are not normally used in VTTC circuits
> because the oscillator tube plate represents a much higher source Z than a
> spark gap switch.  The tank circuit must have an impedance at the Fo that
> matches the plate impedance of the selected tube(s).  Tube circuits, even
in
> high powered coils in the tens of kilowatts often use cap values in the
merely
> 0.002-0.005 uF range.  More L is needed in the tank coil to compensate
compared
> to a disruptive TC with usually larger capacitance.  Mica transmitter
> capacitors are ideal in this tube oscillator application.  'Cheese slicer'
> mechanical variable capacitors with large plate spacings from commercial
> transmitters and antenna tuners are also suitable as a tank cap.  They can
even
> be submerged in oil to increase their operating voltage and capacitance,
or to
> allow a lower voltage cap otherwise unsuitable, to handle the voltage.  I
> suspect that the latest rage, the MMC using polypropylene/foil or
deposited
> foil would be fine as long as the relatively high tank circuit circulating
> current ratings were respected in its design.
>
> The 4-1000 makes a very pretty display tube.  I have one in my display
case.
>
> r stephens
> >
> > ----- Original Message -----
> > From: <mailto:tesla-at-pupman-dot-com>Tesla list
> > To: <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> > Sent: Monday, February 11, 2002 08:59
> > Subject: VTTC capacitor
> >
> > Original poster: "Steve White by way of Terry Fritz
> > <<mailto:twftesla-at-qwest-dot-net>twftesla-at-qwest-dot-net>"
> > <<mailto:slwhite-at-zeus.ia-dot-net>slwhite-at-zeus.ia-dot-net>
> >
> > Are pulse caps suitable for use with a VTTC? I am particularly
interested in
> > their high frequency suitability. Also, has anyone ever built a VTTC
with a
> > 4-1000A tube? Since this tube will handle over 1000 watts, it seems like
a
> > good
> > candidate.
> >
> > Steve: Coiling in Iowa
> >
> >
> >
> >
> >
>
>
>