Re: VTTC capacitor

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

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
>
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