Re: Tube coil, level shifter madness

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

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

John 

What size level shift capacitor are you using?  If you use the 50% power 
rule I suggested earlier, with 2.8kV peak input, here is an equation to
calculate 
proper cap sizing based on 50% peak energy contribution from transformer 
and 50% peak energy contribution from capacitor... 

CLS = PIN / (2 * FPWR * (VPK)^2))*1000000 

Where: 
CLS = Level Shift Capacitor (uF) 
PIN = Average Power Input to VTTC oscillator 
FPWR = Utility Line Frequency 
VPK = Peak input voltage to VTTC oscillator 

This equation is a simplified output of earlier discussion posted 8/22/2000 
and is generally applicable to all VTTC applications.  Capacitor sizing can 
vary +/-10% of calculated with little effect on output. 

Realistic equation for Vpk is 
VPK = VRMS * 1.414 - VFWD diode drop 

VFWD  ranges from 10-12 volts based on number of series diodes in your 
level shift diode. 

Based on above, your level shift capacitor should be around 1uF (1.17uF to 
0.96uF). 

I've hope to have machine up soon to test staccato mode control of a level
shifted
VTTC.  The TTL controls may have been yaking on you, not allowing capacitor 
to fully charge.  Suggest running tube without staccato control on raw AC and
LS 
power supply and see if there is a difference in operation.  This would at
least 
decouple the modulator from the output you are seeing.  Another project in the 
background is the "super-staccato/plate over current protector" PCB to allow 
multiple consecutive "pops" then an adjustable rest period. 

OBTW Carl Willis was running a LS VTTC with staccato control with excellent 
results, (see posting in archives late August 2000).   I wouldn't be surprised
if 
most of your problems are related to the EMI/RFI issues with the TTL modulator.


Happy New Year John! 
Regards 
Dave Sharpe, TCBOR 
Chesterfield, VA. USA 

Tesla list wrote: 
>
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <FutureT-at-aol-dot-com> 
>
> Hello coilers, 
>
> There's been a test I've been wanting to try for a long time.  I figured 
> I wouldn't let the year slip away without doing this.  I finally tried 
> the level shifter circuit on my small original staccato (pulsed) tube 
> coil (16" sparks). 
>
> The power xfrmer has two secondaries; 2kV, and 3.6kV.  I normally 
> use the 3.6kV secondary, but since the lever shifter doubles the 
> voltage, I figured I'd switch to the 2kV winding for this test.  This 
> gave me 4kV.  I'm afraid that 3.6kV x 2 or 7.2kV would be way 
> too much for the 4-250A tube. 
>
> Anyhow, I expected that the output would be a little better due to 
> the little higher voltage, and due to the way that the level shifter better 
> utilizes the xfrmer's capabilities.  Well, the results were disappointing; 
> the sparks were no longer, and the sword-like spark was ruined in 
> the staccato mode.  Rather the sparks became forked and branched. 
> I did not try re-tuning, or anything like that.  Also, the 72LS123 based 
> TTL pulse timer circuit is not too happy with the level shifter.  It seems 
> to misfire at times due to RF interference.  I saw the same thing with 
> the larger staccato coil in the past, and I had to use the 555 timer 
> based pulse circuit at that time. 
>
> Well this goes to show the criticalness of these tube based systems. 
> Everything has to be just right.  Very touchy indeed.  There hasn't 
> been much talk of tube coils on the list lately.  They lack the 
> frantic raw power of a good spark gap system.  I will say though, 
> that the 38" tube coil sparks were a sight to behold.  I do want to 
> build a new high-powered tube coil at some point.  I also plan to 
> build a mostly new spark gap TC to replace my old research coil, 
> which was the precursor to the TT-42 project. 
>
> Onward to the new TC Millennium......   !! 
> John Freau