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Rf Power supply @ 4kV

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Ash Small

Thu Mar 14 2013, 12:06AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Noah Hoppis wrote ...

Still stumbling about the RF though...

Me too. Here's a link to my first thread on this forum:

It may give you some insight into what's probably required for your project.

EDIT: It does go slightly off-topic here and there, but it's still worth reading.

EDIT: It even contains a schematic for a 13.56MHz, 1kW, ~4kV Hartley oscillator (which I'd forgotten). (On page 2, courtesy of Proud Mary)

Noah Hoppis

Thu Mar 14 2013, 05:01AM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

I liked that thread, now I have something to aspire to length wise ;) . I guess after asking several people what I really need is crash course in RF amps. I really haven't found any introductory level info, but I really need ground up basics on power vacuum tube amps, IE schematics of basic class A,AB,B and B push pull, amps with real world explanations. I apologize if I just asked for the world. I tend to do that...

klugesmith

Thu Mar 14 2013, 06:26AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I'm sure the cyclotron guys are keeping an eye on the cyclotron frequency.
Assuming you are accelerating protons, and I did my arithmetic right---
to use 27.2 MHz you would need a 1.8 tesla magnetic field.
13.56 MHz would need only 0.9 T, so the electromagnet power requirement would be 4 times less.

What's a popular field strength on the cyclotron forum?
Anybody using dangerously large and strong permanent magnets?

Ash Small

Thu Mar 14 2013, 11:10AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

klugesmith wrote ...

I'm sure the cyclotron guys are keeping an eye on the cyclotron frequency.
Assuming you are accelerating protons, and I did my arithmetic right---
to use 27.2 MHz you would need a 1.8 tesla magnetic field.
13.56 MHz would need only 0.9 T, so the electromagnet power requirement would be 4 times less.

What's a popular field strength on the cyclotron forum?
Anybody using dangerously large and strong permanent magnets?

Those figures, 0.9T and 1.8T do sound familiar, I've read a bit about small cyclotrons, but only really took notice of any information that might be useful/relevant to my ESLA project (I am planning on using ECR (electron cyclotron resonance) in my ion source, but the figures for electrons @2.45GHz is ~0.0875T, but this apparently has to be adjusted for relativistic reasons, or something, not quite got my head around that bit yet). I did link to 'a wealth of information' on the subject earlier in this thread. I assume it's the 'available' frequencies of 13.56 and 27.2MHz that you'd probably have to use.

The link to the 13.56MHz, 1kW, ~4kV Hartley oscillator article (originally posted by Proud Mary) is here, for anyone who doesn't want to wade through my thread on RF:

It uses a single 3CX1200A7 valve/vacuum tube.

Schematic is here:

Noah Hoppis wrote ...

I liked that thread, now I have something to aspire to length wise ;) . I guess after asking several people what I really need is crash course in RF amps. I really haven't found any introductory level info, but I really need ground up basics on power vacuum tube amps, IE schematics of basic class A,AB,B and B push pull, amps with real world explanations. I apologize if I just asked for the world. I tend to do that...

At least now you're getting somewhere, and you have a better idea of what's involved.

EDIT: I've been doing a bit of reading on Cyclotrons.net.

"Usually beam currents are on the order of microamps at most."

The Rutgers cyclotron (9") operates @13.56MHz and 0.889T.

"The magnet weighs 1780 pounds, it requires 40 volts at 168 amps, 7Kilowatts, to produce the maximum field of 1.2 Tesla. Only 28 volts at 114 amps, 3.2 kW, is required at the operating value of 0.889 Tesla. Water cooling is used to remove the heat generated by the coils, the inlet pressure is approximately 38 PSI and flow rate is no less than 4 GPM. The pressure is controlled with an inline pressure regulator and the flow "

"The transmatch may be recorded as the most home-brewed system of this cyclotron. It utilizes the lumped capacitance of the DEE, which is approximately 70pF, to create a tank circuit out of the chamber itself. Using the resonance equation for an inductor in parallel with a capacitor............ L, the inductance, was chosen to bring the fr to resonance at 13.56 MHz. Initially, coarse tuning was to create an 8 turn coil of length 5 inches, with a cross sectional area of 2.14 inches2, out of Â¼-inch copper refrigeration tubing. The coil was then mounted in an RF tight enclosure known as the RF cabinet. One end of the coil was connected to the protruding DEE stem, while the other end of the coil is connected to chamber ground. Another coil of copper tubing larger in cross sectional area, of only three turns, is mounted co-axially about the first coil. The outer coil constitutes the primary while the inner coil makes up the secondary of the transformer. Adjustable taps were then placed on the primary to locate the 50W loading point. Second order tuning was accomplished empirically. Either expanding or compressing the coil changed the inductance thereby altering fr. Fine tuning was completed at the driving oscillator. Cooling became a necessity when the RF power began to heat the secondary coil such that thermal expansion changed the tank fr. General Electric Dielectrol transformer oil is pumped through the Â¼ inch tubing of the secondary."

Noah Hoppis

Thu Mar 14 2013, 07:16PM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

Updated schematic!!!!! I am fairly certain that I have a new working schematic operating in push pull...

klugesmith

Thu Mar 14 2013, 07:44PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Noah Hoppis wrote ...

Updated schematic!!!!! I am fairly certain that I have a new working schematic operating in push pull...

How does the lower triode work with a negative voltage on the plate?

Ash Small

Thu Mar 14 2013, 09:50PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

The schematic I posted above has been proven to work @50% efficiency. The tube costs @$1000 new, but there are cheaper alternatives that will probably work ok eg 8877, etc. , and I'm sure you could find a second hand one much cheaper from the 'usual sources'.

Why spend ages trying to design your own RF supply, when you can just copy a simple design like the Hartley oscillator I posted above?

Noah Hoppis

Thu Mar 14 2013, 10:11PM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

I though an amp would be easier seeing as one could get a RF signal generator at a ham fest for ~20$. I also though that most generators didn't supply both sides of the sine, above and below 0v. would the Hartley provide variability as well? I need to be able to tune the frequency.

Noah Hoppis

Thu Mar 14 2013, 10:30PM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

And better yet (sorry for double posting) could I use a GU-5B?

Noah Hoppis

Thu Mar 14 2013, 10:37PM

Registered Member #10072 Joined: Thu Feb 14 2013, 05:12AM
Location: seattle wa
Posts: 21

and triple post. Gi 39B? ( keep off it (it's mine!!!!))

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