Glassman cable

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Scott Moroch
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Glassman cable

Post by Scott Moroch »

Today Jack and I went to NJIT with our equipment to begin assembling the entire fusor. Although we have not made an update in many months, we have been making great progress. Recently we tested our glassman power supply and unfortunately, the power supply did not come with the high voltage output cable. The only cable I could find was on ebay, which was has the same model number and connector. However, the part of the cable that goes into the power supply itself is too short. I got the cable for 25 dollars and it is 32 feet long so when I purchased I figured I would take the risk and if it wasn't right, I would alter it. The cable length that enters the power supply must be 8.25" and this cable is 6.25 inches. Does anyone have any advice as to how we should proceed with lengthening it? Should we try to move the connector itself? I will attach images of the cable and power supply. Thanks!


Scott Moroch
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prestonbarrows
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Re: Glassman cable

Post by prestonbarrows »

You can roll your own cables but you will need a fancy die crimper. RG8U cable can be pushed up to around 50kv without too much trouble.

You can see the hexagonal section on yours behind the knurled section; this is originally a circular tube which is crimped on to lock the connector onto the ground braid. The process is quite similar to using BNC crimps.

The very tip does not need that fancy banana plug. Stock glassman cables are literally a metal thumbtack pushed into the braided conductor core. You just need a metal contact to push against a spring on the inside of the supply.

To test the fit, insert the cable into the plug. You should feel the tip hit the spring while the knurled section is not quite touching the base. You can then push in a bit to engage the thread; you should have some play and be able to wiggle the connector and compress the spring freely. As you tighten the hood, you should feel that you never fully compress the spring or bottom it out.

If you cant find the right cable or crimping tools, I would try calling Glassman directly. They know that their supplies last forever and usually change hands a dozen times during their life; they are generally very helpful with supplying manuals/cables and other tech support.
John Futter
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Re: Glassman cable

Post by John Futter »

Scott
The glassman cable is a standard PL259 coax plug with the centre pin drilled out to accept RG8 coax inner dielectric and inner wire.
Glassman does not use a thumb tack but uses a brass washer that has the copper inner through it and the ends splayed before a generous blob of solder is applied to the washer.
Try to get the PL259 with either PE or teflon insulation it is easier to work without breaking as the standard bakelite ones.
The braid is terminated in the usual way in the PL259
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Scott Moroch
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Re: Glassman cable

Post by Scott Moroch »

Thank you both for your informative replies. I will take what you have said into consideration and potentially call Glassman. I will look into the methods you have presented me with. Is there anyway I can simply solder or weld an additional 2" metal rod to the end of the banana plug that is already on there? I understand that it should be insulated with the PE insulator, which is why this is probably not the best idea. I may either buy the PL259 cable or simply try to move the connector back on the cable I have now.

Thank you for your input.

Scott Moroch
"In the middle of difficulty lies opportunity"
-Albert Einstein
John Futter
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Re: Glassman cable

Post by John Futter »

Scott
someone is having you on
the unit seems to have been supplied with a spellman cable
they use the banana plug on the end but the same modified PL259
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Nick Peskosky
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Re: Glassman cable

Post by Nick Peskosky »

Scott,

I have run my Fusor just fine with properly prepared (stripped and double insulated with PVC hose) multi-strand high voltage rated wire from Belden, while not as RF hardened or intrinsically safe as the manufacturer supplied RG8U cables, it has worked just fine for my amateur uses. The Glassman/Spellman units utilize different length connector tubes (these are located parallel to the Cockcroft-Walton multipliers in the rear) based on the units rating but so long as the insulated portion of the cable well exceeds the dielectric breakdown distance of air for the voltages supplied by your unit you should have no problem with kludging an extension onto the banana plug. The jacket and shielding braid of the cable are removed on the connection end anyway so its not likely any extension is going to add to the EMI thrown out of the unit during normal operation. Ensure you have a good earth/star ground for safety and happy fusing!
Nick Peskosky
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Rich Feldman
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Re: Glassman cable

Post by Rich Feldman »

Scott,

I would try extending the banana plug with some 3/16" OD thin brass tube from a hobby shop or hardware store.
The kind that telescopes with adjacent tube sizes.
The ID is a smidge over 5/32" (4 mm) and is perfect for regular banana plugs.

To keep the end on center, apply your kluge skills with electrical tape, heatshrink, plastic hose, or some sort of rigid sleeve.
banana.PNG
All models are wrong; some models are useful. -- George Box
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