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Glassman Power Supplies

Posted: Thu Dec 01, 2005 3:36 pm
I'm seeing alot of positive polarity power supplies for sale on ebay but no negative polarity devices suitable for a fusor. Is it possible to convert one to negative polarity?


Re: Glassman Power Supplies

Posted: Thu Dec 01, 2005 4:05 pm
by Richard Hull
All of this has been discussed before. The answer is yes and no, of course.

Yes, if your particular supply has a "flipper block" inside. This demands the user remove the covers and manually remove often the entire plexglass mounted rectifier assembly and flip it in some fashion so ordained by the manufacturer to reverse the polarity. Fluke and Spellman are particularly good about this in many of their supplies. Unfortunately, those often encountered are usually pretty whimpy on the power end.

No, if the major components throughout the supply are tied to the case ground or chassis or relies on a grounding system that can't be isolated. This is by design.

Yes, if you have the NO supply and are a sharp electronic cookie and willing to ferret or noodle out the methodolgy needed to convert the entire thing.

Don't rely on the marble heads selling on e-bay to understand if the supply offered is switchable as most have just picked the thing up in a junk yard or auction sale for $1.00 and are looking to turn a buck. The probability of a knowledgeable seller in the more complex items category scales inversely with its complexity.

I just bought 2 CD-V700 GM counters off e-bay where the bone heads offered them as being sold "as is"...."unable to test"...."no returns". I know I can fix them as they commonly have zero "beta" PNP germaniums throughout their guts.

It seems the dunderheads didn't see the test uranium sources built in on the sides of the cases or bother to obtain 4 "D" cells needed to make them power up. Had they done this, as I did when they arrived, they could have offered them up as "fully functioning, tested and warranted to function out of box." This would have never let me win them as folks like to hear that and will pour on the bid bucks for such offerings.

Yes, they both worked perfectly, but I was prepared for a couple of losers considering how little I paid.

HV supplies commonly found on E-bay are marginal in voltage but mostly in the current dept. It is rare to see something offered in the 30kv range which also has over 20ma of muscle behind it. Naturally, when you see one, they are, inevitably, positive only supplies with little hope of easy switchover.

Richard Hull

Re: Glassman Power Supplies

Posted: Fri Dec 02, 2005 11:02 pm
by Brian McDermott
Richard pretty much hits the nail on the head. Most Glassman supplies on ebay will be either positive polarity, or lacking in voltage/current. Once in a great while (maybe every 6 months or so), a negative polatity, 20kV or more, 500-1000 watt power supply will show up. The bidding is fierce, and the final price winds up somewhere between $300-$1000 or more. Look for "WX" series power supplies. They are rated at 1000 watts and work great. What's more is that you can make a completely portable fusor system, since the supply weighs only about 30lbs.

Re: Glassman Power Supplies

Posted: Sat Dec 03, 2005 12:51 am
by DaveC
Yup - you change change the board over pretty easily, since the older Glassman supplies, used air insulated components.

All that's needed to reverese the multiplier's polarity is to reverse the diodes. For a 20kV supply, there is probably only 4 to 8 diodes soldered into a rather thick circuit board. Not hard to do this part. As we have discussed here at length, it is current monitoring, HV display and a few other items, that might be tricky to hook up with plus and minus reversed.

I used to have an 80kV Glassman, with both polarity multipliers.
To change you just removed and swapped out. For that matter, making the other polarity is not all that difficult, if you can get hold of the right caps, diodes, and resistors. You can just follow the other board's layout but put the diodes in reversed. (arrows pointing down the stack.)

If you are serious about buying one from ebay, despite Brian's experienced note about the bidding, you would do well, to speak directly with the seller to be sure about the construction.

Dave Cooper