The AM Forum

I am curious what those of you who are homebrewers are using for high voltage wire, as in high power transmitter use.  I am rebuilding a 1930's AM transmitter, a massive 600+ pound Frankeinstein thing on two open Western Electric telco CO rack frames.  The 1920's fabric and tar insulated high B+ lines are just as terrifying and deteriorated as the open construction is.  Around 4 KV. 

Once upon a time I would go to the local auto supply store and buy a roll of solid core stranded spark plug wire, I think it was branded "Packard."  But today?  I also used to buy it from JC Whitney by mail, and yes, they still exist, but seem clueless when searched for solid core bulk spark plug wire.

I do have a new spool of Belden CRT anode cable, modern red stuff with something like 50 kv breakdown.  But it doesn't look "period correct" on the old Frankenstein rig and I vaguely seem to recall someone didn't like CRT anode wire in this application, I forget why. 

So...has anyone run across a source of high voltage wire that is similar to spark plug cable and doesn't cost a small fortune?  I am being a typical cheapskate ham on this project.

WB6NVH said:I have a transmitter of about the same time period and type that you have mentioned. Regarding the CRT anode wire, from old days in the TV repair shop, (now there is an anarchism!), that wire was very rigid and in some cases if kinked it could break the insulation and have an HV failure there. I recommend going to an electrical or HVAC supply house and purchase silicone ignition wire that is used for oil burners and such. We have a large scale fume incinerator onsite, (often referred to as a TOU: Thermal Oxidizing Unit ;) ), that utilizes that wire for the igniters and LV burners.

I used spark plug wire in my homebrew rig. JC Whitney isn't the only supplier of spark plug wire. Got it off eBay, cost me $17 for the amount I needed.

Packard 440 is available and Moroso, Mallory etc still offer solid core wire.  Try to get copper core rather than steel core. For lower voltage sections you might look into probe wire.  18ga but only rated to 5kv.
14ga GTO might also fit some applications for you but check the ratings (15kv?).

I got some of this from Amazon:

https://www.amazon.com/dp/B01IX3B8YC?psc=1&ref=ppx_yo2ov_dt_b_product_details

Chicom, of course, but looks good. The core solders well and the jacket doesn't melt, so it seems to be silicone, as they promise.

I have also been using the Amazon HV wire. Solders well and is quite flexible.

neon sign wire

Digikey has 10kv hookup (test probe) wire in colors.

Modern production cloth-covered spark plug wire in the 9mm diameter is available on eBay and looks the part.

I use it without any worries.

73DG

How about a few photos of this monster! Sounds very interesting

This is all good info.  I should have been searching for "ignition wire" or "ignition" cable it seems. The red wire on Amazon looks perfect for my newly acquired Globe King 275 and the black stuff for Frankenstein.

I have put some photos of Frankenstein below.  Rescued from the Craigslist tube and scrap transformer vultures.  As far as I can tell, it's a pair of 250TH's modulated by a pair of 250T's and driven by a pair of RK-31's.  We think built around 1937.  Despite being at the height of the Depression, the guy must have had some money. A panel meter was real money and this has a lot of them.  The plate transformer is a 4800 Volt pole pig that has been drained and coated with glypt 80 years ago.  Lots of reverse engineering to do. Two racks, Western Electric open frame telco CO style, solid steel.  It took three of us to get these racks into my truck and me a week, alone, to pull decks and unload them in sections.  Probably at least a KW out.  You can see the open construction at that voltage level goes beyond scary to terrifying.  Those 30's hams were made of strong stuff.  I am pretty sure this guy had no indoor pets.  I will be reverse-engineering it and drawing diagrams for a awhile, and intense use of the grid dip meter is on the way.  Note that some parts are missing as are many tubes.  866's abound.

More photos

Keen eyes will note a deck that doesn't belong at the top of the modulator section.  This is something my benefactor found later from the estate and put there.  It is actually an RF section from another transmitter which uses (probably) a 100TH driven by 6L6's or similar and some smaller tubes, in other words the exciter and PA all on one deck.  It looks like the oscillator may be self excited so I expect to sound like late night Cuban CW DX on 40 meters in the 1960's if I get it going too. The PA tank is AWOL on it.  Looks promising for getting a ticket from the FCC or a nasty note from an ARRL OO.

Sharp eyes will also wonder about the screened porch at the power supply deck (bottom) of the RF rack.  As I am fond of saying now, this is not where you shovel in coal, even though it is in that condition, but rather contains four (Or six? I forget) 866's that either wouldn't fit behind the panel or else were intended as a fancy light show when on the air (probably the latter.)  

I did remove all the fragile tubes before transport.  I think the whole load was around 650-700 pounds.

The last high voltage wire I purchased, solid core ignition wire, came from Summit Racing. Fortunately they are only a couple of miles away. Of course, that means DX Engineering is very close as well. Such a temptation!

Bill KA8WTK

Check out this wire dealer.

http://www.magnetoparts.com/wire.htm

I've bought from that company.  Good stuff, good guy. :D

73DG

I use RG59.

Shielded for your protection and you can find it at 5kv rated.  I've shoved a lot more than 5kv into the 5kv rated stuff off ebay.  Like, double that.

SHV connectors work with it just fine.

--Shane
WP2ASS / ex KD6VXI

Use AWM type GTO. It's rated (I think) for 15 KV. Neon sign installers use it. I;'ve seen it in 14 18 and 22 gauge. 18 is nice. Look on Amazon. Some electrical supply houses might have it or a shop that installs neon signs. Beware of automotive wire as most so called spark plug wire today is a carbonized fabric conductor (so called resistance wire). Seth KC2WE