[TCML] Big VTTC Suggestions Wanted

[Dr. John W. Gudenas]

Philip
James gave you some good tips. If you want to design a VTTC properly  
you need to look at the tube characteristics.
As James indicated, you need to have proper impedance matching with  
the tank circuit and tube. He needed a high impedance primary for his  
power triode.
This achieves a balance between the tube and primary. I mentioned this  
earlier when discussing my pancake grid coil and some discussion  
followed on tube characteristic curves.
You can tweak almost any VTTC into running, but how efficiently is  
energy being transfered to the secondary or wasted in heat energy in  
all the other components?

A big note on tank capacitors. At your voltage and energy levels you  
need a really robust tank capacitor. As James indicated and I have  
experienced the same, if you over current or over volt
mica transmitting caps, they explode in a dark gooey disgusting mess.  
I ended up using RF composite micas in series/parallel combination at  
40kv. I suppose you can cal it a multi-maxi-capacitor bank.
These caps are three inches in diameter and five inches long with 1/4  
20 bolt terminals on each end. I can run for 30 minutes and they don't  
get warm.  Some RF rated high current ceramic capacitors work too.
I have not tried the extended foil  MMC, but if you do, make sure you  
account for both current and voltage. Incidentally, a lower frequency  
VTTC ( 150kHz - 200kHz) is easier on the tank cap.

If you design your coil so that there is proper impedance matching  
with two 833A/C it will work fine, but no matter what tube you use it  
is sure to suffer failure if you substantially over volt it.
Your 7200 v PT will likely put out 10kv peak to peak. This has got to  
spell disaster for an 833A/C sooner, later or instantly!
I hope this helps.
John W. G.

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


On Oct 2, 2008, at 7:58 AM, Phillip Slawinski wrote:

> Hi All,
>
> I'd like to build a large VTTC.  I'll probably end up going with a 6"
> secondary since I have 6" PVC already.  I can get my hands on 7200V  
> PT to
> use for the tank power supply.
>
> What kind of K value should I be aiming for?  Is there any reason  
> why I
> would not want to use a larger triode instead of multiple 833Cs?
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John W. Gudenas, Ph.D.
Professor of Computer Science