Re: tank circuit of VTTC

["David Sharpe" <sccr4us-at-erols-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Herwig, David, All
I listed pertinent info in previous posting.  Will post spec info from previous
post to help...

The 833C is the graphite version of the tube we love to abuse.
The 833D is a new tube that has been on the market for about a year.
The 'D' have much longer fil life expectancy (4000hrs vs 2200 for a 'C').
and much higher reserve emission capability then the 'C'.
The tubes have the same dynamic specs as the original 833A, the specs
that are different are listed below...

                833A            833C            833D
Fils V        10VAC        10VAC        10VAC
Fils I          10A             10A               11.5A
Plate P      350/450*    400/550*       450/600*
Cost           $105            $115            $128
Shipping and Handling <$20 for 2 tubes

*Forced Air Cooling, ICAS ratings, 40CFM at seal between plate and grid.

The reserve capacity of the C and D would suggest 600mA for C and
up to 650-700mA for the D at 4kV.  The maximum recommended
input power is still 1.8kW, but if you abuse the tube slightly, the 833D
for short duty cycle should be capable of 2.4kW input each.  This would
suggest up to 4kW output for a pair of tubes in either series or push-pull
(tank input).  The 'D' is a MOOSE, and a deal for $128.

As a side note, at E. Wingate's Teslathon this weekend, on Ed's VTTC;
two 833C's running approximately 4-5kW input at 4-5kVAC NEVER
showed any sign of red hot heating on plates with a 5 minute + runtime with
output streamers in the 28-30" range.  Was observed by at least 12  folks
Saturday night...

Regards

Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "Herwig Roscher" <herwig.roscher-at-gmx.de>
>
> David Trimmell wrote to the list:
>
> > but the 833C is around 400 Watt.
>
> David,
>
> So, it's an improved version.
>
> > I use a small muffin fan pointed at the tubes and primary for
> cooling on extended runs
> - I'm using a 28 W fan trying to blow air through the valve socket in
> order to keep the temperature of the base seal low. As the holes in
> this socket are relatively small, the cooling isn't very effective.
>
> > I have run the 833's up to 5500V without internal arcover.
> - You are daring. ;-)
>
> > > 4. Is there any rf bypass for C1?
> > Not sure of what you mean? All grounds are a common RF ground, so the
> > filter cap should bypass most RF to ground.
> - Some VTTC coilers use additional bypass caps as these filter
> caps don't offer a low impedance for rf.
>
> > > 6. In the schematic your tank coil is not tapped. How did you
> > > manage the tuning?
> > Let me apologise, my schematic still needs some work, values are from
> > memory, not notes. I designed the MMC to give me a "close" value, and can
> > tap up or down the string, not perfect, by far.
> - No problem! I'm intending on achieving the tuning in the same way.
>
> > Here you are in new territory, I have not gone over the 5KV mark much.
> - Of course I could use lower plate voltages as well, but I've got the
> components for a 10 kV PSU already and the tube cries for HV and
> high power  :-))
>
> > Just watch the temp and perhaps forced air (from bellow) would
> be good.
> - I'm planning on air cooling the MMC (first) and the secondary as
> well.
>
> Regards,
>
> Herwig