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Re: [TCML] Proper VTTC Coupling? (coil specs)

The 4-125A power tetrode should work fine. It is a VHF tube and the plate voltage is 3kv so a doubled MOT won't kill it. However, consider using perhaps 14 awg or 16 awg for the primary as 22 turns of 12awg pvc is going to make a solenoid around 5" -> 6" high on a 9" secondary. This is bound to cause some sort of problem, particularly if the grid coil is above it. With this small coil you might consider putting the grid under the primary.

With a .00005uf tank capacitor the current in the tank circuit should not get very high as long as the secondary is tuned to the primary frequency and you can use the energy in the secondary and dissipate it with the discharge. That is why I believe
you can use 16 awg or 14 awg on the primary.

As long as you have a good supply of pico farad micas you should be able to tune it in. It will certainly be sensitive. If you have an HV air variable from a kilo-watt ham rig it may be useful.

Interesting coil, let's see what happens.
John W. G.

John W. Gudenas, Ph.D.
Professor of Computer Science

On Oct 18, 2008, at 8:13 PM, futuret@xxxxxxx wrote:

Dr. John,

Thanks for your comments.  The full specs of the planned
small, simple coil are:

Tank cap, mica  0.0005uF or as needed to tune

secondary, 2.5 x 9 inch, 28awg (600+ turns)

primary, 4.5" (?) dia, 22T of 12awg pvc insulated wire

grid coil, 4.5" dia, 18T of 26awg on a sliding form

transformer, small MOT with level shift doubler

small 2.5" dia toroid (maybe)

vacuum tube, 4-125A with socket

filament transformer as needed

grid leak resistor, 30W variable up to 4k ohm

misc, bypass caps, tube cap, hook up wire, hardware, etc.

Base, wood at first to test everything

variac, external

I'll try both the grids tied together method, and maybe
the screen grid fed by a dropping resistor method.  I'll
tap the grid coil at 12 turns or so for use with the tube
grids-tied-together method.  I'm considering using a
811A tube or some other tube  rather  than the
4-125A tube.  I may test various tubes in the coil.

I'm trying to decide whether to use a 4.5" dia primary
or a 4.75" dia primary.  The 4.5" form is thick PVC,
the 4.75" form is plexiglas.  I already have the secondary
coil from previous work.

I may use the coil to research various configurations, etc.
It should make a nice demo coil if the design works out well.


-----Original Message-----
From: Dr. John W. Gudenas <comsciprof@xxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@pupman
Sent: Sat, 18 Oct 2008 6:59 pm
Subject: Re: [TCML] Proper VTTC Coupling?

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