[TCML] New 833C VTTC - poor performance

[Kris Grillo <kristianisawesome@xxxxxxxxx>]

I just finished my first VTTC. It's a single 833C closely following Steve Ward's single 833A schematic. The specs:
Secondary - 3.5" x 17" x #26
Topload - 2" x 7.5" toroid, about .25" above the top turn.
Primary - 29 turns #12 THHN on a 6.25" green pipe. Bottom turn level with secondary bottom turn.
Filament supply - rewound mot, 10V even (does get warm).
Plate supply - very large (physically) old mot, shunts removed, voltage doubler 2.05uf, mo diode, 2nf10kv ceramic disk
Tank cap - 2nf 40kV TDK UHV doorknob
Plate filter - 12 turns #12 on 50ohm 20W
Feedback coil - 20 turns #26
Grid leak - 4k 125w variable, 2nf 40kV TDK UHV doorknob
Everything is wired with #12 wire. All connections are tight.
No staccato yet

For some reason, I can't get past 6" - 8" arks and about 75 volts in from the variac without the plate starting to glow orange. I've tried 24 - 20 turns on the feedback, 20 - 31 turns on the primary, varying the grid leak resistance between 1K - 4K, varying the feedback coil from .5" above the primary all the way to 8" above. I tried going with 1.75uf and 2uf on the votage doubler. I tried a 4" pvc secondary with 19.75" of #26. I know the 833C can do better than 8" arcs. It's a brand new Taylor from RF parts, by the way. 

I'm out of ideas. Anyone have any suggestions?

Thanks
Kris



      
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