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Registered Member #10072
Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21
I need a power supply with two 811a triodes (or one) that gives about 4kV. It is going to be driving the dee(s) in a cyclotron, so no real current will be spent. The requirements are that one dee is + charged then the other dee is + charged (the charge could be negative, more info on cyclotrons). There could only be one dee but it would need to be + then - in rapid succession.This is a bit of a different animal than amps I've dealt with in the past. Any help would be greatly appreciated. i have attached a PDF of the supply so far... ]cyclotron-supply.pdf[/file]
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Hi Noah, It's good to see you here.
I'd suggest either using a microwave oven transformer, with the doubler circuit (microwave oven capacitor and microwave oven diode), to give you the 4kV (you could use the power supply from an inverter type microwave oven instead, but these circuits are more tricky to 'hack')
I'm working on a circuit that uses one of these setups to charge a capacitor to 4kV, then using a valve (vacuum tube) to power a magnetron for my ion source (to give more control over the magnetron, a bit more complex than the 'simple' circuit I've outlined on Cyclotrons.net). If you are just powering the 'D's' in a cyclotron, I imagine this setup would give plenty of current for your requirements.
I hope this suggestion helps.
EDIT: another possibly better option, which I think is used with some cyclotrons, is to add another capacitor to increase the capacitance of the 'D's' (add the capacitor in parallel), and add an inductor to form a resonant 20MHz circuit.
(I think synchro-cylcotrons utilise a variable capacitor, so that the frequency can be increased as the particles accelerate.)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Below is a push-pull Colpitts power oscillator, and is a tested design for driving a 50 kW 120 kHz full-wave C&W multiplier. I know very little about cyclotrons, and their needs, but I'd guess that a circuit on these lines would be used for driving the Dees in a bare bones design. The inductance of the RFCs, the values of C, and the push-pull transformer properties selected will depend on the operating frequency required.
I see from the 811A datasheet that it has an absolute maximum anode voltage of 1500V when used as an RF amplifier/Oscillator. Clearly, it will be destroyed quickly if you try to run it at 4 kV.
The costs and labour of building a cyclotron are likely to be such that it would be a completely false economy to try and build one using microwave oven transformers and incorrectly specified valves. With all that pumping down, vacuum instruments, shielding, dosimetry, and all the rest it will probably cost as much as a new car, and very much more if you live in a country where the design, construction, and operation of particle accelerators is controlled and regulated by law.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Below is a push-pull power oscillator, and is a tested design for driving a 50 kW 120 kHz full-wave C&W multiplier. I know very little about cyclotrons, and their needs, but I'd guess that a circuit on these lines would be used for driving the Dees in a bare bones design. The inductance of the RFCs, the values of C, and the push-pull transformer properties selected will depend on the operating frequency required.
I see from the 811A datasheet that it has an absolute maximum anode voltage of 1500V when used as an RF amplifier/Oscillator. Clearly, it will be destroyed quickly if you try to run it at 4 kV.
The costs and labour of building a cyclotron are likely to be such that it would be a completely false economy to try and build one using microwave oven transformers and incorrectly specified valves. With all that pumping down, vacuum instruments, shielding, dosimetry, and all the rest it will probably cost as much as a new car, and very much more if you live in a country where the design, construction, and operation of particle accelerators is controlled and regulated by law.
I was wondering if the 811a was up to the job, but thought I'd leave that bit to someone more knowlegable than myself on these matters. I believe my own research into 4kV+ valves has brought up a few, I think one is the GU5B, from memory.
I understand that (in UK, at least), any device that accelerates particles to an energy of less that 1MeV does not require licensing.
The only 'expensive' part of a cyclotron is the magnet, vacuum systems can be put together quite cheaply, especially if you use a diff. pump. Guages can be obtained cheaply (I've at least a dozen assorted ones, along with some controllers, etc, and I've only spent a total of a few hundred pounds on my system)
If an MOT supplies sufficient current, and they can supply several hundred watts even after losses, and you need 4kV, why not use the 4kV supply from a microwave oven? It leaves more of your budget to spend on the magnet. (and suitable valves/tubes)
(I understand, from reading a thread on another forum, that Noah is considering winding his own coils for the magnet, and that he can obtain copper for scrap value. As most of the expense is the copper for the coils and cooling pipes, this could well end up being the cheapest ~8" cyclotron ever built.)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Yes, I believe there is a good choice of Soviet-era RF power triodes to be had on ebay, Mr Ash.
As for what you call licensing, in the European Union particle accelerators of less than 1 MeV do not require prior design approval, site inspection &c. before construction can begin.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
As for what you call licensing, in the European Union particle accelerators of less than 1 MeV do not require prior design approval, site inspection &c. before construction can begin.
The type of cyclotron Noah is considering building is 'portable', although you'd need lifting gear to move the magnet, and maybe the 'D's'. At these power levels, cyclotron radiation/bremhstrallung radiation is only an issue if you are accelerating electrons.
Registered Member #10072
Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21
Yes the device would be fairly small, and I don't worry too much about radiation ( though it will be run remotely...). This is similar to a linear amplifier, and the design was so that I would have two outputs for the two dees but one would work for one dee, and I have been over doing it trying to get + and - signals. what would I do if I just used a GU5B? the 811a's would be out of phase and only amplifying one side of the wave, and thus only seeing 2000V. Anybody have a design for a GU5B single tube linear amp?
Registered Member #10072
Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21
it doesn't have to be a linear amp; to be frank I know very little about amplifiers, only that triodes could be used. all I know about amps came from the feedback circiut in my recently constructed 572b VTTC. Really I just need help finding a simple HV amp.
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Rf Power supply @ 4kV
