Magnifier 13 report

From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Thursday, April 16, 1998 3:43 PM
To:  Tesla List
Subject:  Re: Magnifier 13 report

Hi Richard,
             I'm going to follow this one with a great deal of 

> From:  richard hull [SMTP:rhull-at-richmond.infi-dot-net]
> Sent:  Wednesday, April 15, 1998 8:34 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Magnifier 13 report
> All,
> Here is the first pass data on the H2 thyratron switch excited magnifier 13.
> This was a cobbled up test of the new circuit coupled to the new large table
> top magnifier.
> Statistics of system:
> Coil driver-  Primary: 13 turns of #8 THHN insulator wire tight wound and
> tapped wound over top of the secondary for a K=.65-.78 based on tap point.
> Taps are in steps from 32uh to 89uh.
>              Secondary: 44 turns of #14 stranded TW wire- insulated. 910uh
> total inductance.  Natural 1/4 wave frequency 1210khz. covered with 2 wraps
> of 20mil polyethylene and overwound directly with primary.
>              Coil form is 1/2" wall 16" diameter schedule 40 PVC 8" tall.
> gap system/tank circuit:
> gap effectively placed across a 0-7kvdc supply (current limited- 60ma).  A
> .007ufd 20kv pulse rated capacitor is used as the driver tank capacitor.
> Gap was a 5C22 hydrogen thyratron with grid drive circuit supplying a 3 us
> 300 volt pulse into 50 ohms.  This circuit was triggered by a 555 astable
> oscilator which had over three decade range of pulse adjustability .1hz-2khz.
> Insturmentation:
> Pearson wideband current transformer,  Tektronix TDS 310 digital storage scope
> Observations:
> The current transformer indicated about a 50 amp pulse in the tank with
> 6KVDC applied.  The pulse was a single ping of 3us (thyratron pulse on time)
> with no ring within the primary (thyratron is turned off with the reflex
> from the magnetic collapse of the primary magnetic field  This is not seen
> on the CT due to circuit opening within 100 nanoseconds after current pulse
> zero crossing.  In short the primary was hit and never rung up.  A slug of
> magnetic energy was dropped in the primary coil and then open circuited.

At the lowest tank inductance, I see the 3uS is commensurate with a 
full cycle of ring at the tank resonant frequency. I gather the 
thyratron didn't reignite despite the length of this pulse? 

> The scope was next placed about 8 feet from the system with a 12" whip for a
> terminal in a BNC plug in channel 1 of the scope.  Depending on resonator,
> the peak voltage recorded on the damped waves was 55v peak or 110volts pp.
> It was noted the resonators rung for as many as 51 cycles per pop. showing
> maximum Q was realized and there was no swap back and forth interaction
> between the primary tank circuit and the driver secondary or the resonator.

What voltage (if any) was left on the primary cap following gap 

> This being the case, and as expected, the tuning of the primary made
> absolutely no difference or had zero effect on the output frequency.  This
> frequency was rigidly fixed as being that of the resonator alone and was
> verified with scope measurements. The tuning did, as expected, influence the
> current in the tank with the lowest tap inductance sending the tank current
> to about 150 amps while the highest inductance point reduced it to about 40
> amps.  (Changing the effective surge impedance of the tank)  The sparks were
> thin and whispy and never exceeded three inches. (~70 watts input)  This
> system was not optimized as it was thrown together on a first pass.
> More data as things happen here.

That is a mode of operation the Corums emphasize on their literature. 
Nice to have a gap that can actually do it :) It would be interesting 
to compare peak output in this mode with peak output using a normal 
gap. Can be done?

> Richard Hull, TCBOR