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VTTC + glasfiber form

Original poster: "Herwig Roscher by way of Terry Fritz <twftesla-at-uswest-dot-net>" <herwig.roscher-at-gmx.de>

Hi all,

I am running a VTTC, driven by a power tetrode. Plate voltage is 10 
kV filtered DC. The primary coil was wound onto a 8" PVC form. 
After some time I faced serious and deep carbon tracks starting 
from the upper end of the winding. In addition this part of the form 
changed its color and became black, liquid and stinky.

Marc Metlicka was so kind as to send me one of his glasfiber 
forms for tests. Here are the results:

This form is excellent in every way: Light, stable, concentric, 
The wire could be wound nicely and glued to the form easily. 
Coating with polyurethane was possible as well.
It could be shaped quickly with a metal saw, a file and sandpaper.

What I did:

In order to increase the tank impedance further more, I changed the 
number of turns from 67 (old form) to 74. As I substituted the PVC 
insulated housewire by magnetwire of the same cross section at 
the same time, the heigth of the winding decreased from 7.3" to 4" 
now. No carbon tracks any more.

Despite of using an additional 6" PVC screening tube between 
primary and secondary coil before, I couldn't stop flashovers 
between the coils. Now, as the primary coil is much shorter, I 
could remove the screening tube without getting flashovers (up to 

The glasfiber form gets rather warm (a lot of power is transfered), 
but not as warm as the PVC form. And the glasfiber form doesn't 
get weak at all. I'll drill some holes (between the coils) into the 
medium-densitiy-fiberboard, the coils are mounted to, in order to 
force the air circulation by generating a kind of chimney cooling.

I am very satisfied with this glasfiber form. Another problem solved - 
thank you very much, Marc!