High Voltage Multiplier (VM) with x-former System

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Dennis P Brown
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High Voltage Multiplier (VM) with x-former System

Post by Dennis P Brown » Sat Oct 08, 2016 3:23 pm

Here is the completed HV multiplier de-rated using a microwave x-former (MWX); for safety, the MWX has been isolated via a HV cap (part of one stage of the voltage multiplier) and all put in a grounded metal case. In this manner, the high voltage/current MWX is restricted to just a 900 pF output of the cap. This output, in turn, is feed into the 5 1/2 stages of the upper VM (the other cap & diode are on that section.) This VM will be rated to only 25 kV and used to excite the belt of the very large Van de Graaff (VdG) generator I built some time ago.

The VM, when two more stages are added, and a NST is used to excite it, can reach 100 kV but that will not be attempted unless, and until the VdG is tested and either works or does not for the deuterium accelerator /deuterium gun project.
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VM_25kV(3).JPG
MV and Power Supply unit (Note white door knob cap inside x-former housing/case)

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Rich Feldman
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Re: High Voltage Multiplier (VM) with x-former System

Post by Rich Feldman » Sat Oct 08, 2016 9:26 pm

Looking good there, Dennis. Thanks for sharing.

One comment about your acronyms. Looks like you figured the term NST is well-known & didn't need explanation, but then chose to use MWX for "microwave x-former". In the HV hobbyist community, I think they're generally called MOT's. And you must be familiar with XRT's, for higher voltage than NST's.

For me, the term Microwave Transformer (or M. Capacitor, or M. Diode, unqualified by the word Oven) means a component intended and specified for use at frequencies higher than 300 MHz. Here's one real microwave transformer:
minirf-1.jpg
You can find things like that in TV antenna/cable accessories, like splitters and baluns. Also in any 10/100/1000Base-T ethernet (LAN) port, often integrated into the connector that's mistakenly called a RJ45.
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Rex Allers
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Re: High Voltage Multiplier (VM) with x-former System

Post by Rex Allers » Sun Oct 09, 2016 8:25 am

Rich, I agree in principle with your general premise, but I must argue many of the details.

I've always understood the lower boundary for microwaves to be at 1 GHz (1000 MHz) and 300 MHz is far below that. The wire-wound ferrite transformer you showed might work into high hundreds of MHz but near or beyond 1 GHz, I don't think transformers exist.

At microwave frequencies any magnetic coupling is more a sub-part of EM wave interactions. Passive circuit elements begin to be described by their size, shape, width, spacing, etc. I don't think I've ever heard of a transformer at these frequencies. Various magic configurations of transmission line couplings might make impedance transformations similar to transformers at lower frequencies but that's a rough approximation.

So I agree with your criticism of the acronyms, but not with your subsequent explanation of a "microwave transformer", which I don't think exists.
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Rich Feldman
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Re: High Voltage Multiplier (VM) with x-former System

Post by Rich Feldman » Mon Oct 10, 2016 9:38 pm

OK, the gauntlet has been thrown. :-)

I concede that only the broad definitions of microwave extend below 1 GHz. Just did some Googling (actually Binging) and drew a chart with things I learned. Shades of pink indicate overlapping definitions of microwave.
bands3.JPG
bands3.JPG (18.27 KiB) Viewed 2127 times
And it was disingenuous to have cited 1000Base-T (which handles 1.00 Gbps over Cat 5 cable up to 100 meters) because its symbol rate per twisted-pair line is only 125 Mbaud.

But conventional discrete-element circuits, and hybrids that also include some of that mysterious magic stuff, are found in the low GHz range, especially for broadband functions.

Here, from Mini-Circuits catalog, is a directional coupler for 800 to 2000 MHz. http://www.minicircuits.com/pdfs/ZNDC-13-2G+.pdf
coup.JPG
Someone had an old mini-circuits p/n with the same specs on ebay, and posted pictures of the guts. ZADC-13-2000-1 http://www.ebay.co.uk/itm/Mini-Circuits ... 0209833363
coup2.JPG
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