How does one ascertain the plate current of a vttc?

[DominicMOT]

I am at a loss to think of how. I’ve researched elsewhere, to no avail. On Steve Ward’s website he says that you must assume a current you want the tube to pull from the plate supply. What does that mean in practice?

[Mads Barnkob]

I did a few design calculations, from John Freud and Steve Ward, in my VTTC1 article: https://kaizerpowerelectronics.dk/tesla-coils/kaizer-vttc-i/

Power consumption is basically down to Ohm's law, when considering the tube to run in CW mode at its specified maximum plate current.

In my example, I got two 811A tubes in parallel, that makes for 0.35A maximum plate current (175mA each) and being fed from a single MOT with voltage doubler, I have 3200V on the plate at 160VAC input.

P = 3200V * 0.35A = 1120W.

In reality, I measured this to 900W at 3800V, phase shift, staccato precision or other influences could lower this figure. But its close enough to choose the size of your power supply.

You will properly use a staccato controller, to get 1-50BPS synced to the mains frequency (or 1-60 in 60Hz countries) and by that, the average power draw is considerably lower.

[DominicMOT]

Thanks, this helps a lot!