Wi;;
Richard Hull built a small thyratron switched TC about 20 years ago, so it
can be done.
The output was an anemic 5-7" sparks IIRC, and the supporting electronics
to control
the thyratron was nearly as involved as a DRSSTC. For bang for buck, a
DRSSTC
would significantly overwhelm a thryatron operated coil...JMHO...
On Sun, Apr 20, 2014 at 3:00 PM, Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx>wrote:
> Hi Wil,
>
> Tesla coil primary circuits are designed to "ring" over at least several
> cycles in order to allow complete energy transfer from the primary to the
> secondary. Most thyratrons are designed to conduct current only in one
> direction. And even those thyratrons that are designed to handle somewhat
> oscillatory currents cannot directly handle the high-Q ringing seen in a
> Tesla Coil primary circuit. If not protected from reverse current flow,
> the thyratron's cathode will be permanently damaged as ion bombardment
> blows off the cathode's emmisive layer.
>
> Thyratrons are normally used with Pulse Forming Networks (PFN's) that
> provide a unipolar output pulse, and not the oscillatory currents in a
> primary circuit. If you simply want to generate high voltage pulses, you
> can make your own PFN (a ladder network of capacitors and inductors)
> charged by a HVDC source. The PFN is connected through the primary of a
> closely-coupled pulse transformer and to the anode of the thyratron. When
> the thyratron is triggered, a relatively square HV pulse is generated on
> the secondary side of the pulse transformer. The PFN is often "resonantly"
> (re)charged through a HV choke and HV diode such that it's stored voltage
> is about 2X the supply voltage. A good discussion of DC resonant charging
> can be found on Richie Burnett's site:
>
> http://www.richieburnett.co.uk/dcresist.html
>
> A schematic showing how a thyratron can be used to generate a series of
> HV pulses can be seen here:
>
> http://www.pocketmagic.net/2011/03/thyratrons/#.U1QVd0K5ZSl
>
> You can use a thyratron in a TC primary circuit using a similar circuit.
> In this case, you'll need to connect a string of high voltage high current
> bypass diodes across the thyratron to handle reverse current flow. You
> would also substitute a primary tank capacitor or MMC instead of the PFN. A
> trigger pulse of sufficient width (or a series of timed trigger pulses) are
> used to trigger and re-trigger the thyratron during the entire "ring up"
> period of your Tesla Coil. The tank cap current is conducted through the
> thyratron during one half cycle and the bypass diodes conduct during the
> next half cycle, allowing the primary circuit to ring. Once the thyratron
> trigger signal is removed (ideally after secondary ring-up), the thyratron
> stops conducting.
>
> Although permitting precise switching, thyratrons are actually quite lossy
> (lossier than spark gaps!), so you may need to be careful about not
> exceeding RMS current and overheating the tube. The ringing time in a TC is
> usually much longer than the typical pulse times in PFN pulsed power
> applications.
>
> Good luck,
>
> Bert
> --
> Bert Hickman
> Stoneridge Engineering
> http://www.capturedlightning.com
> ***********************************************************************
> World's source for "Captured Lightning" Lichtenberg Figure sculptures,
> magnetically "shrunken" coins, and scarce/out of print technical books
> ***********************************************************************
>
>
>
>
>
> William Howard wrote:
>
>> Dear Group,
>> I have a large thyratron I purchased years ago and want to build a coil
>> with it.
>>
>> Does anyone have a schematic for a relaxation circuit around (to suit a
>> tesla coil)? I was think of using neon bulbs after a megaohm resistor to
>> create a relaxation oscillator to trigger it.
>>
>> I used florescent bulb starters once after a megaomh resistor to trigger a
>> relay which dumped 400v from a 20000uf capacitor bank into a ignition coil
>> which had a capacitor in parallel to the primary. It would produce a loud
>> thump every 5s and a large discharge about 5cm...
>>
>> The relays soon died but the discharge into the concrete was impressive :)
>>
>> Hoping to pull off the same thing again but with a higher cyclic rate. I
>> want to produce impulse currents.
>>
>> Any ideas would be welcome. I only have mots for a power supply...
>>
>> Cheers!
>> -Wil
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>>
>>
>>
>
>
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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