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Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
I still don't understand how it could work. When the device is switched on, current flows until it drops to zero, it can't be switched off. Perhaps the tetrode version would be more successful as Harry suggested, but it still looks iffish.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It seems to me that the problem is not so much whether modulation can be applied - since both pulse repetition frequency and pulse position modulation are both options with a thyratron - but that such modulation could not be directly de-coded by the human ear, when applied to a 'singing arc' and so on.
What it might sound like is anybody's guess. A rasping buzz I suspect.
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Coronafix wrote ...
I still don't understand how it could work. When the device is switched on, current flows until it drops to zero, it can't be switched off. Perhaps the tetrode version would be more successful as Harry suggested, but it still looks iffish.
You can think of a hydrogen thyratron as a fast thyristor. Most thyratrons (other than specilly constructed "hollow anode" types) can only safely conduct current in the normal direction, and forced reverse conduction (arcing) rapidly destroys the cathode of most thyratrons. Since a TC primary requires bidirectional conduction over several cycles during ring-up, you can reverse-connect a HV rectifier or even an identical reverse-connected thyratron (with the grid floating or positively biased). The reverse conduction device was sometimes called a "hydrogen diode". When the control thyratron is triggered, primary current flows through it during the positive current half cycle and then through the reverse diode during the negative half cycle. During the negative half cycle, anode current drops to zero and the control thyratron turns off.
If, at the end of the negative cycle, the control grid is still positively biased, the control thyratron will again turn on for the next positive half cycle. If the control grid has been switched to a negative bias during th first negative half cycle, the control thyratron will stay off, opening the primary tank circuit. By applying a positive bias for a duration sufficient to permit full ring-up, ideal (1st notch) quenching can be achieved. Because of the rarefied hydrogen atmosphere, forward conduction losses tend to be significantly higher than for a regular spark gap operated at STP. However, the hydrogen thyratron should permit better triggering precision and quenching control. Thyratron switches for Tesla Coils have been mostly a curiosity - mostly just to see if it can be done. HV IGBT's can provide much lower switching losses.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
I see now, I was getting myself confused as to where the interruption needed to be. DC, as you said Steve would be the best bet. A reverse thyratron would be necessary otherwise it would sound as Harry said like a rasping buzz. Thanks for the concise explanation Bert, I know that silicon is ideal but some thoughts were started and I wanted to see if it was possible or if anyone had done it. The control circuit could be difficult if you wanted to take into account quenching efficiency as well, not to mention switching two thyratrons.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Even if this is an old thread, the question needs an answer. Here are some results in building a thyratron switched tesla coil (THYTC): More pics here:
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Thyratron Coil
