Re: Spice simulation pictures

To: tesla-at-pupman-dot-com
Subject: Re: Spice simulation pictures
From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
Date: Sat, 19 Oct 1996 00:28:21 -0500
Date:          Thu, 17 Oct 1996 22:25:01 -0600
From:          Tesla List <tesla-at-poodle.pupman-dot-com>
To:            Tesla-list-subscribers-at-poodle.pupman-dot-com
Subject:       Re: Spice simulation pictures
Reply-to:      tesla-at-pupman-dot-com

> > Subject: Re: Spice simulation pictures

>From hullr-at-whitlock-dot-comThu Oct 17 22:20:40 1996
Date: Thu, 17 Oct 1996 10:41:39 -0700
From: Richard Hull <hullr-at-whitlock-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: Spice simulation pictures

Tesla List wrote:
<mega snip>
>
Bert wrote:
 
>... Another thought - are any tube coilers using heavy top-loading (other
> than Robert Stephens' 15 KW oil immersed beastie)? Sounds like it would
> make these systems less sensitive to detuning from operator movement.
> You could still control breakout threshold via a "bump" on the toroid.
> 
> -- Bert --

Richard Hull wrote:
>Bert,
>
>In theory a tube coil could be top loaded.  I have never seen one with 
>even a 1" ball on it!!!!  These systems are very sensitive to capacitive 
> top loading.  Remember a tube coil is just an oscillator in which the 
>primary and associated coupled grid coil are merely part of the delecate 
>oscillator tank.  Any loading on the top of the coupled secondary would 
>require a major re-think back in the oscillator circuit which is rarely 
>equipped with the broad tune range devices needed.
>
>I eagerly await the first guy to have a 18"X4" secondary on his tube coil 
>with a 20"X5" toroid on top to step forward!!!!
>
>Richard Hull, TCBOR

Richard, 

Would a 24 inch by 3 incher please you?  Been there, done that.  Oh 
BTW, no streamers.

One important aspect characteristic of vacuum tube Tesla coils which 
is not often considered because it is not an issue with disruptive 
coils is the duty cycle of the circulating current in the secondary.  
Didn't someone (Bert?) recently post that the disruptive system has a duty 
cycle of some 0.03%?  In a vacuum tube coil operating from a full 
wave filtered DC power supply the secondary circulating current is 
100% CW RMS toaster  watts power.  At 100 kilovolts the resonator
circulating current starts climbing rapidly as you add a little topload 
capacitance to your vacuum tube Tesla coil. 

I made a 100pF cap which sustained 150 KV before 
breakdown from a 50 US gal steel drum and a smaller metal cylinder 
with rounded ends suspended inside.  I wound a secondary out of #14 AWG
enamelled copper wire on a 6 inch PVC form that resonated with this 'topload'
at 150 kHz and drove it with my 1000 watt vacuum tube oscillator
(3 x 810 triodes). 
 
I was able to swing the 100 pF load to about 85 kilovolts RMS (120 kV 
peak).  The secondary winding got so hot in just 120 seconds of operation that
I shut the system down for fear of melting the PVC tube on which it was 
wound!  My circulating current was 8 amps RMS according to the 
measured output voltage across a capacitive reactance of some 10.6 K 
ohms, but the heat produced in the wire felt more the equivalent of 
maybe 30 amps RMS.  Can anyone explain where my figuring leads to 
such an error?  The interconnect between the top of the secondary and 
the drum capacitor was #14 PVC covered solid wire.  It got bloody hot 
too.  If I had had one then, that's where I would have liked to place an RF 
thermocouple ammeter.

The commercial client who I am working on the large vacuum tube 100 
kHz system for with the oil filled resonator wanted me to consider 
also building them a system whereby I would be able to swing a 100 pF 
load to 200 KV RMS at 1 MHz.  This is a formidable power challenge.  
Using the same figuring based just on voltage divided by capacitive 
reactance the continuous secondary resonator circulating current this time
would be 125.63 amps RMS!  This is a job only for large copper ribbon or 
tubing with silver plating.  I declined on the big 1 MHz project BTW, at least
until I get more high power CW experience.  How about these guys with the 
vacuum tubes in the linear accelerators developing nearly three 
quarters of a megavolt at 50 MHz across a ten turn helix with a 50 kilowatt
tube oscillator.  At least they don't have to swing a big toplaoad capacitance.

Food for thought, and actual projects for the well funded mentally deranged.

rwstephens