Re: VTTC -715B - Part II Modelling

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

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

Ed, Tesla List

Any info you can get me on drive and auxiliary circuits for this guy (similar
5D21, 4PR60) would be greatly appreciated.

I've also done some additional modeling with Multisim V2001 and what
appears to be a good solution is assume that a PP Hartley oscillator would
have a tank impedance of 2X tube impedance (15kV-at-15A ~ 1k ohm;
therefore 2000 ohms.  If you build a 10 mesh pulse forming network (PFN)
consisting of 400mH inductance X 100nF capacitance per mesh will result
in a pulse width of ~ 4-4.5 millisecs, Zo ~ 2000 ohms.  Charge to 21kV (15kV
X 60mA NST through a capacitively coupled voltage doubler, then grid
modulate 715B's on.  Vbb during pulse is 10kV, pulse current 5.5-5.8A
average peak power during pulse a whopping 55-58kW!!!  PRF in the 3 / sec
range results in average power in the 162W range (tubes is 60W X 2; I know
I'm pushing them   :^)  ), AC burden is 800-900W.

The only fly in the ointment is the PFN inductance 10 mesh at 400mH is going
to be BIG unless you wind with microscopic wire, then your parasitics take
off to the moon.  What if you wound as a pi wound plate RF choke on a
1/4 to 1/2" PVC tube and stuff ferrite's in the core to boost coupling and
inductance.  Will this reduce size sufficiently to make the idea practical?
100nF capacitors at 25kV is a stretch, but could be built using MMC type
technology to reduce losses.  The modeling suggests that a PFN with long
pulse widths becomes physically very large (HUGE ???) compared to the
rest of the components in the VTTC.

Tank capacitors appear to be a similar issue with high voltage, Vtank peak
would approach 10*2*0.84 or 17-18kV using PP hartley configuration
(I'd use 25kV rated capacitors at least).

This looks very intriguing to the R&D engineer in me (can't do it at work,
might as well do it home), and I like the challenge of leading for a change,
rather then building the same old thing...

Any feedback from the "brain trust" would be appreciated.  :^)

Regards

Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "Ed Phillips by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>
>
> Tesla list wrote:
> >
> > Original poster: "David Sharpe by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>
> >
> > Terry, ALL
> >
> > Got lucky today at Richmond, VA Frostfest and picked
> > up five (5) NOS Raytheon 715B tetrodes for nearly
> > nothing, still in original boxes.
> >
> > I know they were used as a hard switch radar modulator
> > tube, and are right robust looking for the tubes physical
> > size.  Any idea where I can get basing info and at
> > least plate voltage, current and fils specs?  They might make
> > an awesome Super Staccato breadboard coil, and if they
> > are related to 4PRXXX series, could really handle the kV
> > and pulse current.  Thanks...
> >
> > Regards
> > Dave Sharpe, TCBOR
> > Chesterfield, VA. USA
>
> Dave:
>
>         If you haven't found what you want by the time you get this, let me
> know and I'll send you enough to get you started.  Those tubes were
> intended for ~15 kV hard-tube magnetron pulsers, and take an awful lot
> of drive.  I suspect they would be interesting for a self-excited VTTC
> using a rectified NST or set of MOV's for power supply.
>
> Ed