Re: 3-1000z coil, more questions

["David Trimmell" <davidt-at-pond-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ross,

Looks like you are out to make a quality VTTC. I'v a couple comments,
though:

On Mon, 31 Jul 2000, Tesla list wrote:

> Original poster: "Ross Overstreet" <ross-o-at-mindspring-dot-com> 
> 
> 
> I'm still working on the 3-1000z tube coil.  I have updated the schematic to
> include most of the suggestions you guys provided.  The schematic is still
> missing some RF chokes, but I'll draw them in as soon as I figure out how to
> make them.  As you can see from my tube page
> http://users.better-dot-org/roverstreet/projects/tube_coil/tube.htm, I have the
> platform complete and have started bolting things down.  Guess I'll jump
> right into the questions.
> 
> 1.  My secondary is 4" x 23 5/8", wound with 0.021" magnet wire, and has a
> measured resonant freq of 400 KHz.  (This is surprising b/c Medhurst &
> Wheeler predict it to be 375 kHz)  I have a handful of 2500pF, 30KV doorknob
> caps that I planned to use in the tank circuit.  I plan to use 12ga THHN
> wire (.135 OD) wound on a 6.25" PVC pipe for the primary.  When I started
> running the numbers, looks like I can get near 400kHz using one of the
> 2500pF doorknobs and around 18 turns in the primary.  Are these
reasonable
> numbers?  Should I aim for less primary turns and more C?  More L and less
> C?
> 

Those Doorknobs will work, but at the power level you will be operating,
they will run hot. And you know what that means, the C will wander. I
sugest using Mica caps or a Polly MMC. I use the Panasonic caps in a
single string (the 1600V ones) and find that at around 2KW they do get
warm, but at least the capacitance doesn't stray, causing tunning
problems.

> 2.  I don't really understand what the grid-leak network is all about.  I
> have a good understanding of disruptive coils but this triode stuff is
> making me feel dumb.  It would really help me out if someone could give me a
> general overview of what is happening in the typical triode TC circuit.
> 

Looks like John's reply got this one...

> 3.  Anyone see anything terribly wrong with the schematic (other than wrong
> values in the tank circuit and lack of chokes)?
> 

You are showing that you plan to run with filtered DC, this may give you
the impression of poor performance, as sparks will be short and
flame-like. I would sugest using a level shifter (as Dave Sharpe, John
Freau, myself and others have used with success) this meathod is described
on my web site and in the archives. No chokes are nessisary if you use AC
to the plate and let the tube self-rectify.

> 4.  I know that the leads from the filament transformer to the tube should
> be short.  Is 2.5ft with 10ga wire too long?  I can mount it under the top
> deck right near the tube if I need to.
> 

As john pointed out, lead lengths here are not really important, as long
as you measure proper voltage to filaments.

> If I ever figure this !-at-#$ thing out I'll be sure to thoroughly document it
> on my page so others can come up to speed more quickly.
> 

Looks like your the guy to do that! Like you site.

Regards,

David Trimmell
www.ChaoticUniverse-dot-com

> Thanks,
> Ross-O
> 
> 
> 
> 
>