Re: grid-block, was 811A any good?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 1/27/01 6:13:12 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

>  >will go into conduction, oscillate, and pulse itself off.
>  > 
>  > Aharrrrr!  The "Squegger" !!!
>  > 
>  > Great name for a VTTC project :-)  Just what I was intending
>  > to do with those 813s!
>  > 
>  > If I recall correctly, around 150-200k for the grid leak and
>  > 150-200pF for the grid cap.  Need a high time constant so
>  > that the charge on the cap builds up and biases the tube
>  > (hey, I'm learning the language ;-) to cutoff.  What say
>  > you, Ed?
>  > 
>  > Dunckx

Dunckx,

I used that method for my first pulsed coil which used 845 tubes.
These tubes are rated for 1200 volts, but I applied about 4500
volts.  The tubes worked fine in normal operation, but the kickback
during the pulsed (I called it the "sputter mode") operation, tended
to cause an arc-over in the tube base, which destroyed the metal
to glass seal, and destroyed the tubes.  I fiddled later with this
sputter mode using more suitable tubes, but never got it to work
as nicely as I wanted.  The sparks tended to be a little dim, and
rather branched, so I switched to the staccato idea.

John