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Re: [TCML] New 833C VTTC - poor performance
check to be sure the TDK tank cap is rated for RF current and is not a DC
filter type cap.
you may also have to experiment with the position of the grid leak coil ---
sometimes it is necessary to have it 6-10" up the sec coil for best results.
measure your grid drive current to be sure you are driving the 833 properly.
On Fri, Aug 1, 2008 at 12:05 PM, Kris Grillo <kristianisawesome@xxxxxxxxx>wrote:
> 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?
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