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Re: [TCML] Big VTTC Suggestions Wanted

On Thu, Oct 2, 2008 at 20:15, 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 guess what I've heard about these Micas being indestructible is not true?
Or is it just a case of a VTTC being harder on the caps?

> 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.

This is what I planned on using.  I should be getting 20 caps from DC in the
near future.  I have a mica transmitting cap on my 833C coil, but it's only
2nF.  I do have some .026 uF Maxwells that I could use.

> Incidentally, a lower frequency VTTC ( 150kHz - 200kHz) is easier on the
> tank cap.

Oh really, why is that?

> 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.

Well based on what information I've been given today I don't think I'll be
using 833s for my large tube coil.

> 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
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