The AM Forum

What is the best type of wire to use for plate connections?

I'm thinking of large high voltage tubes like MV rectifiers, modulators, and RF finals.

I'd like to use something with high insulation that can withstand several KV just as a safety precaution.

I have some neon sign wire that has 15KV insulation, but the trouble with it is it's very thick and stiff.

Using it is bound to put a force on the plate caps which I'd like to avoid.

I'd like to find something with high voltage insulation, but very flexible. Maybe like the wire used for meter probes -- but probably higher voltage.

Dave

Like this?

http://www.mgs4u.com/RF-Microwave/high-voltage-wire.htm

Other than Steve's good suggestion, you might try vintage auto parts stores online.  HV old fashion spark plug wire works well.  In the old days, they did not use resistance wire but rather just finely stranded copper wire.  The stuff that I saw some time ago was very flexible and came in various colors. 

Joe, W3GMS

I purchased some old-style spark plug wire at an antique tractor meet some years ago.  It uses what looks like normal stranded tinned copper wire, what you would expect to see in hookup wire, about 22 ga. with a heavy layer of rubber insulation, and the whole thing is covered with varnished fabric.  It is flexible, easy to work with, and takes solder readily.  Not sure whether or not it is the same stuff Joe is talking about. The guy I bought mine from said it was made specifically for restoration of 1930s vintage tractor engines, identical to the original.

Meter probe wire is rated only for about 5 kv, and after a short while the warm environment inside a transmitter dries out the insulation, and it begins to crack and crumble.

Which is why the spark plug wire would be perfect for the job, since it is designed to withstand high temperatures from an engine.

I use the inexpensive outdoor luminous tubing wire and it is 14 GA stranded (19x26) and only a little stiff, but after preforming it to shape it puts no pressure at all on the MV tubes and has been satisfactory. The whole thing about putting tension on the MV tubes is related directly to the length of the piece of wire, a longer piece with a little slack or a bend in it is fine. It is rated 15KV RMS, which is really more like 21KV. It is black and looks nice.

This kind (above) costs 20 cents per ft in a 250 FT spool, which is what I bought.
http://kcelectronics.com/gto-15ignitionwirerated15000voltssuppliedin250footpullbox.aspx


There is also a more flexible "HI-FLEX GTO-15" which has a silicone core with a PVC jacket that sells for about 70 cents a foot in a 250 Ft spool.
http://www.partsforsigns.com/Neon_GTO_Wire_250_ROLL_p/hi-flex%20gto-15.htm

But avoid modern day automotive spark plug "wire".  It is not really wire at all; it is more like a track of carbon dust enclosed inside insulative tubing.

Packard 440 spark plug wire. It's the same stuff as the fancy stuff with the woven outer sheath. Just no fancy schmantzy woven coating.

Packard 440 in my big supply.

Use good quality stranded wire of suitable gage.  Route it through acrylic "fish tank" airline tubing, seal ends with a dab of RTV or Hot glue or wire tie or what ever. RTV over the terminal ends.

Easy to find and low cost.

Hot Rod red or clear sparkplug wire sold for those dressed up flatheads is OK for DC and audio but none of that type of stuff is any good for RF.

For RF at anything over 100W or so carrier use #12 or larger. For high power and especially 20M and up use 1/2" copper strap from the plate choke and blocking cap to the tube assuming your using something useful like a pi-network. Insert the parasitic suppressor right next to the plate cap.

If you insist on using series feed and plug in coils then do what the OT's did, steal what they could at the dump or beg from an electrician.....you see some of that construction on here also ;D but then again most of those cant get above 75M anyway :D

Carl

Carl, you don't need, or generally want, a heavy conductor for a tube plate connection.  The plate lead carries relatively low current compared to an output tuned circuit, for example. .  A lossy plate lead can even be beneficial in reducing VHF parasitics.

I chose the plate lead for it's mechanical properties, like flexibility and heat tolerance.  Usually I use fairly small braid like RG58 shield or Teflon insulated stranded wire.  I don't worry about insulation because noting is ever going to touch it.  Lots of good suggestion for HV wiring here, but they are generally stiffer than I like for a plate lead.

Maybe one of these carries what you are looking for. temperatures from 150-450 deg C, silicone and others, up to 40KV, some is made of as many #30 strands as necessary to be the right gauge.

http://www.daburn.com/2636HighVoltageSiliconeRubberLeadWire200CVW-1.aspx

http://www.worldwidewire.com/silicone-wire/silicone-braidless-UL3239.htm

http://wire.thermalwire.com/category/ltage-wire-single-conductor-450-176-c-to-150-176-c

There is also an anti-corona version of this stuff. If the voltage is on the high side it might be worthwhile because the silicone will last longer. Excessive corona will 'burn' the silicone from the inside and make it brittle over time but the usual 'ham' voltage range of 2-3KV it is not much of a concern.




For fun, the old handbooks have pictures of RF and power wiring. Silicone didn't exist back then but air did!

Most of the transmitters look like they used a thin bare solid wire and the power supplies and modulators a thinly insulated stranded wire.

The wire in the transmitters usually looks rather straight or taut while the stranded stuff has curves in it.

The old stuff was lower voltage, 1000-2500 or so, but the voltage issue is only spacing.

DF:  max voltage?  RF or not?

For my front panel plate ammeter at 1.2kV I use RG58 with the shield grounded to avoid electrical fileds nearby.
Modulated (2.4 kV) plate voltage under chassis travels on RG58 without shield and additional insulator tube (of low quality, maybe unnecessary).
This is of interest:
http://daytona.tunl.duke.edu/pipermail/sneap/2008-March/002440.html   (30kV?)
Above the 4/65 A the temperature is too high for plastic insulators. Only ceramics or glass tubes or nothing.
I think that it is not necessary to look for anything else.

In one of my HB transmitters I use HV wire taken from a parted-out BC-339 military rig.  It is #14 solid tinned copper, with about 1/2" diameter rubber(?) composition insulation, covered with unvarnished fabric.  The whole thing was originally encased in flexible lead conduit tubing.  I didn't want to deal with trying to snake the lead conduit through the transmitter, so I removed the lead sheathing.  Pretty easy; just slit it down the side and peeled it off. The lead conduit preserved the decades-old insulation perfectly, so that it looked like it had just come out of the factory.  Still have a gallon can full of scrap lead round here somewhere.  I did not have quite enough wire for all the HV wiring inside the transmitter, so I finished the job using the antique tractor spark plug wire described above.  

When I was in Africa back in the 60s, I stripped down five BC-339s and shipped home some of the lighter weight parts.  Left the rest in the scrap yard where the locals recycled the metal. I could now kick myself for not pulling out and saving that HV wire; five of those transmitters would have given me a lifetime supply.  Also left behind four 900/900 pf, 2000 volt Cardwell split stator capacitors because I thought they were too heavy and would have cost too much to ship all five of them 10K miles.  So, I have a good reason to periodically kick myself twice.

Say WHAT?

Thats 180 degrees out from good engineering practice even at 27 MHz. Now Im talking KW amps here and not a 807 where a #20/22 lead from a resistor part of the suppressor is fine.
OTOH since many on here dont operate above 3885 there may not be the need to build to 10M specs and needs but even low power AM BCB transmitters dont skimp on the plate leads.

I use GTO-15 HV wire. It's a 14ga fine strand wire insulated in a thick silicone jacket rated at 15kv, and costs usually 40-50 cents a foot online. It's the mainstay of the neon sign biz as well, so I would try putting a call into a sign shop in your area and ask if you can scoop up whatever you need. I did that with a shop in town here, and he gave me the remainder of a 500ft roll, which had about 80ft left on it for a 20 dollar bill. It's good stuff, and doesn't dry rot.

73

Just noticed Op already mentioned the GTO-15 wire. Sry about that. :P

Is OK, no one reads my posts.