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Re: 'Toll free' gets blasted with 6 kv !
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Solid-core spark plug wire -- Packard 440 or similar -- is the way to go.? It's extremely durable, reasonably flexible, and good to well over 25 kV.? If you're not comfortable with that, you can easily open up some braided ground strap or strip some coax and run the wire through the [grounded] braid.? With that setup, there's no way that your HV is going to reach out and touch someone.? Unless, of course, you do something stupid and/or careless...
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...Some years ago, I was working on a megawatt-class amplifier.? The driver stage required 6 kV at six Amperes, and there was an issue which required me to disconnect the HV from the driver stage.? The 6 kV supply output was through a maroon, screw-on Millen connector, which was 100% reliable at 6 kV.? I dutifully unscrewed and removed the HV lead from the supply and performed the tests.? When I entered the amplifier to reinstall the lead, everything was fine until the lead got close to the output connector.? The "BANG!" in the enclosed space left me momentarily deaf, and the flash left a black spot in my vision for several minutes.
It turned out that the bleeder string(s) on the 6 kV supply had opened up, leaving about 900 Joules (50 microfarads) to find ground in a few milliseconds.? To this day, I'm very glad that it hit the lead and not my hand; and I always, ALWAYS have used caution -- and chicken sticks -- since that event.
By the way, fixing the bleeder problem solved the issue which started the trouble. Edmund Watts
ed_watts@... -----Original Message-----
From: jim.thom@... [ham_amplifiers] To: ham_amplifiers Sent: Thu, Dec 20, 2018 5:43 am Subject: RE: [ham_amplifiers] 'Toll free' gets blasted with 6 kv !
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Drake uses em on the back of the L4B? RF deck, but the HV lead? coming out of the loom is like the center conductor + poly off of some 8-U coax? and? it's really short...and max of? 2650 on it..on rx.?
I used the damned things on the hb supply, with 6.7 kv, then sold it to the buddy with the YC-156 amp u see on the pix page.? ?He redid them , this time on the side of the cabs,, and mounted to? some? square? HV? micarta...+ nylon screws.?
When I had it, one day the line V went up to? 247 V..and? B+? rose to a hair under? 7 kv.... and it arced from center to? one of the 2 x SS mounting screws !? ? ?Also, when I got my arm? within 1' of the silicone rubber coated belden 10 kv test prod? wire, all the hair on my arm stood on end, which really? freaked me out.?
Most of
these? HV connectors have one issue or another.? ?Even the Alden ones are not perfect, and are easily pulled out, no locking? provision.? ? The better types use a braid over the dielectric, like? 393 /213? etc, and are configured such that the braid /shield? always makes? contact? 1st..... just b4 the center? conductor? connects.?
On this latest? B+? supply I'm building,? I'm hard wiring all the B+? connections, where the 393 cable goes external? from the HV supply, over to the 2nd cab, which contains the C1 -L-C2? filter, then more? 393 over to the 3rd cab, which contains the RF deck.? Then lugs on the center conductor and braid, strain relief? with a plastic clamp? on a 1" diam stand off, then more strain relief where it exits the cab with those rubber? reducing fittings, that cinch down on the? cabl
e.? ?I'm done with hv connectors,? they all have some kind of? drawback, or are bulky.?
On the inside of the cabs, I used plane jane Belden? 10 kv rated? test prod wire,? 18 gauge, with the silicone rubber insulation...super flexible.? ?Good on the inside of a cab,? but I would not use it external, not robust enough, and silicone rubber is too easily pinched, nicked, etc.? You could slice into it, and the cut slit would self heal, and you would? never know there was a cut into it.?
I have? 200' of 393? coax, with its teflon dielectric over the center conductor and also over the silver plated braid.? ?Then ground the braid at each end.? ?Then a? separate 10 / 8 gauge, insulated wire,? with lugs on each end,? bonding the cabs together.? ?I only need a few? feet for the external? HV wiring.?
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div>On that YC-156? supply, besides a HV meter in both the HV supply, with its 4 x oil caps etc,? I also had a HV meter in 2nd box, with the? 20 x lytics..and a 3rd? HV meter in the RF deck.? ?IF? HV fuse blows open, the HV meter in the RF deck drops to zero, while the other 2 x hv meters? still reads 6.7 kv.... being on the inboard side of the HV fuse.? ?Also wired 2 x? green neons in series, then wired that mess across the last lytic in the series string, at the cold end.? Works good, and you can see the pair of green? neons? ?from? 50'? away.? ?Good visual? attention getting device.? ?Any box that has HV inside, gets a HV meter.?
Another problem with the millens is there is no provision for strain relief.?
Jim? ?VE7RF?
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