Magnifier 13 report

From:  richard hull [SMTP:rhull-at-richmond.infi-dot-net]
Sent:  Saturday, April 18, 1998 1:19 PM
To:  Tesla List
Subject:  Re: Magnifier 13 report


>> 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.

> Malcolm asked...
>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? 

That is correct!  But.... the highest frequency I can tune with the primary
circuit is 25uh with .007 cap or about 350khz which is about 3 us.  The
precise time of the current pulse is 2.5us  The grid pulse is 3.2us but the
70 % point takes about 500ns to reach for firing.  The minimum firing grid
voltage is 150 volts or so for the 5C22.  Remember this is no vacuum tube
and has a severe positive grid characteristic.  You gotta' pour on th' coals
high positive to get this puppy to blast off.  I am well within the 300v/us
risetime spec. with my self designed pulse transformer and SCR capacitive
discharge firing circuit.  The grid drive is not trivial.  volts aren't
enough......dv/dt and source impedance are also tightly spec'd.  RH

>> 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.
Malcom asked...
>What voltage (if any) was left on the primary cap following gap 

Haven't measured that, but should be close to zero as reverse flow in the
thyratron is impossible and there is no reverse path for feeding the
primary's reflex energy back to the capacitor. RH

>> 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?



I realize that this is indeed the Corums mode of operation.  The coil,
unfortunately seems to be un tunable!!  I have not tried the micro critical
tune that Tesla noted though and will hook in an antenna tuner coil to
carefully vary that parameter and get back to everyone with a report.

Richard Hull, TCBOR