Re: Tube coil with 833A

In a message dated 99-07-09 01:57:32 EDT, you write:

<< Hello.
> As some of you may remember, I was considering
> buying the 833A triode. Now I have a "working" construction
> with it giving 4" sparks, running with a 500W mot, 1.6 kV plate voltage.
> I would like to know how long it normally takes until the plate gets
> its bright orange color. I have a large sharp-edged hot spot in the center
> of the both 
> sides of the plate only five seconds after power-up. Is it normal?
> I've also tried to use the thing as an induction-heater - no success.
> Janne >>


The sharp edged red spot suggests to me that the coil might not
be tuned or loaded precisely.  Any redness should be more spread 
out over the plate, although it will always be brightest at center.  The small
MOT with 833A should be able to give about 9" or 10" sparks, although
the one time I tried the tuned grid...the sparks were shorter...maybe
6" or 7" or so.  Also, with the tuned grid setup, the plate coil depends
on reflected impedance from the secondary coil to give a proper
impedance match, so it may help to vary the coupling to see what's
best.  I didn't spend much time with the tuned grid arrangement.

With a 700W MOT and a level shifter (doubler) circuit using the
original MOT diode and cap, an 833A can give 20" sparks, using a
tuned plate arrangement.  Details are in the archives.

John Freau