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dsavitsk 31st July 2007 09:28 PM

High Voltage Insulator for Umbilical
I am making an umbilical to connect a preamp and a power supply. There will be 4 wires to carry the B+ (~300V), G, and heater supplies. Does anyone have a suggestion on an outer coating for the wires to act as an additional insulator?

SY 31st July 2007 09:43 PM

What's wrong with normal sleeving? This isn't terribly high voltage. You could even use shrink. For the neurotic audiophile, the bundle could be wrapped in teflon tape, then shrink applied.

kevinkr 31st July 2007 10:14 PM

Where abrasion is a concern I slip the high voltage conductors into some aquarium tubing and generally slip the whole bundle into expandable braided black sleeving for appearance and strain relief. In nearly 20yrs I have not had a problem with this approach, looks better than heat shrink and far more flexible. A little heatshrink tubing at the ends and nice cpc style connectors from action electronics and I am done..

zigzagflux 31st July 2007 11:45 PM

Nice ideas, both of you.

I am somewhat preferential to the military gray Amphenol solder pot connectors. Overpriced? Absolutely.

I do not have audiophile nervosa, but in the 18 years of field service working with test equipment, I have had less than stellar results with the Amp CPC connectors. Just a little too weak in those instances where repeated connect/disconnect cycles each day trash the little captive pins. Never a problem with the Amphenols.

Granted, a preamp sees "little to none" duty cycle, so is probably just fine. Audiophile nervosa, no, but anal retentive, maybe a little.

I would also consider buying an oversized 6 or 8 pin connector, and use an "in the clear" pin for the B+. i.e. the pins surrounding the B+ pin are unused. Just a thought. You don't pay much more for the extra pins. A little heatshrink on the B+ solder pot end doesn't hurt either. Easy to pull off if necessary.

dsavitsk 1st August 2007 01:43 AM

Thanks for the replies. I picked up some Amphenol connectors from Mouser. They weren't too expensive and seemed like a good idea. I only got 4 pins, but as you say it the isolated pin seems like a good idea. Of course, if PSUD is to be believed, B+ ripple will be in the uV range, and heaters are also regulated DC, so I don't imagine there will be any issues.

I think I will just put a layer of heatshrink on the wire, which is teflon coated on its own, though I like the aquarium tube idea -- I'll look into that. The paranoia is not audiophile related, but more that I am pretty paranoid about fire. I always go into this with the assumption that I have done something wrong, so I try to over compensate for safety. I have amps that have been running fine for years that I still won't leave running if I am not around.

SY 1st August 2007 01:51 AM

Actually, I think Kevin's mesh idea is excellent and will probably do that for my next build. The last thing I built with a HV cable was my phono preamp, and it uses CAT5.

nhuwar 1st August 2007 03:33 AM

Hi dsavitsk if youthink about it most hook up wire is good to 600 vdc so fire isn't a real concern.

But for the sake of safety you can never go to far. I think as long as you use teflon heat shrink you should be golden.

I'm thinking about seperating church and state for my amp I'm working on sence the power supply alone will tip the scales at 50+ pounds.

For b+ on the output tubes i am going to use rg58 with mhv connectors.


kevinkr 1st August 2007 04:07 PM

On the CPC thing, while they are not as rugged as the milspec amphenols I haven't had any problem in commercial service in over 10 yrs of use.. They are rated for at least a few hundred insertion cycles which should be enough for the life of most hifi equipment, and being locking are far better than the octal and jones plugs I still see all too frequently applied by inexperienced hobbyists.

The main reason I avoid the metal connectors besides the high cost is that they are quite heavy/klunky and when moving equipment around an inadvertent collision of a swinging connector (captive cable) with the chassis and there goes your nice paint job..


Incidentally anyone using non-locking connectors should use an AC interlock on that connector to assure that the supply will not operate when the cable is not plugged in. And there should be no exposed contacts either particularly if the supply can be energized with the load disconnected or in general. (Plug/socket gender issue.)

dsavitsk 3rd August 2007 06:24 PM

For the record, these Amphenols are what might be termed as freakishly huge. The Mouser catalog did not do them justice -- they seem to expect a garden hose to act as the conduit ...

Anyhow, I know people (SY in particular) don't like the use of XLR connectors as power connectors (SY likes to say it is when, not if you will plug the wrong thing in the wrong place) but I can't get my 3 prong audio connectors to connect to the 5 prong XLR connectors I bought for power a while back, so I may just use them here. The Amphenols may have to wait until I build something larger and more military ready ...

Bandersnatch 4th August 2007 12:42 PM

I just trusted the wire's insulation. These are for an amp running to 600V of B+, with AC to the filament iron and bias( 8-pins ). The B+ wire is 1kV rated and the rest is 600V. All are stuck in some heat-shrink. The connecters are the Amphenol MS-series. Pins rated to 700VAC between themselves. The switch is on the amp's chassis, and they control a relay coil in the PS, and 6.3V heater TX for the front end tubes.

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