Re: Grid R/C pulsing of a CW VTTC

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

Original poster: "David Trimmell by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>

Carl, Yes I know what you are talking about with those AF noises, mostly 
horribly shrill! But with the right capacitance (using the 50K ohm) I could 
get a true 10 to 40 pulses per second (estimated, as I didn't measure), 
only instead of the nice sword like sparks from the cathode lifting method, 
I got thicker gnarly ones. Interesting was that I was able to get 12 
inchers. The same setup with "true" staccato Level Shifting gave me 16" 
sparks with one 304TL.

I think there may be some problems with using the 556 timer SCR cathode 
lifter with DC mode, as there is no 0 crossing, maybe some other problems? 
Sputter mode with DC to the plates was pretty stable, but did show some 
tendency to drift (as seen on the scope). I really did not spend that much 
time on this. It was just something I had thought about some time ago, and 
with the DC setup for the Audio mod work, I thought I would give it a go.

Yeah, its all "experimental" for myself as well, and I only barely 
comprehend the theory behind these things (Vac. Tubes)!

Regards,

David Trimmell

At 03:52 PM 2/26/01, you wrote:
>Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" 
><cwillis-at-guilford.edu>
>
>
>Hi David,
>
>Sounds like your're doing some neat stuff these days...
>
>I think you're right that there's no problems with using the sputter mode if
>the coil is DC driven.  I used this method on a small 211 based coil a while
>back to make squealing, thin strands of discharge (corresponding to a
>high-frequency blocking action.) As I recall, the grid leak resistance 
>used was
>nearly 100 kOHM!  You can tune the RC to make different AF noises in the
>discharge and different discharge effects.
>
>For DC coils, this may be a way to affect "super staccato" action- using 
>both a
>cathode-grounding staccato circuit (maybe just an SCR switched by a signal
>generator since no phasing issues occur) as well as a high grid RC for higher
>frequency pulses within the main staccato pulse.
>
>In my experience, staccato control of my current (level-shifted, AC) 833-A 
>coil
>gave a slight spark-length and thickness improvement over sputter mode.  As
>well as causing the sputter action, the high gridleak RC may adversely reduce
>the actual oscillator conduction angle.  I never went into the mathematical
>analysis of how blocking works, it was all experimental for me.