What are the Correct Pins or Plugs for Thordarson Transformers?

[Todd, KA1KAQ]

After resigning myself to the blown mod iron in my transmitter, I remembered a unit I picked up at a hamfest many moon ago. It's a Thordarson Multi-Match modulation transformer, T11M78. Specs posted on the AM Window site show it as a 500w unit.

But it has no studs for attaching the cables. Instead, there are 6 brown porcelain insulators on each end with holes in them. These accept some kind of plug or pin. Standard banana plugs are too big.

I do have some of the tiny version, picked them up a couple years back to use for making ARC-5 connectors. They fit the transformer also, but don't seem to be a good choice since they don't make a lot of contact. It's not a loose fit, but barely what I'd call snug, and certainly not as tight as I'd think would be required in such service.

Curious to know what others have used on these transformers. I was thinking maybe there was some kind of a pin that fits, with a threaded stud on the opposite end, but that makes too much sense.

[k7yoo]

I went out and looked at the transformer shelf--I have one of those with the connectors in place-the transformer is part of a complete modulator unit.
a) I will measure and give you details on the connectors
b) I will check stock
c) I will mail them to you--if I have them
d) I will do it tonite
e) how loose is loose?--you aren't jump starting a pickup!!

Skippy

[Ed-VA3ES]

Grab a bunch of RCA plugs, the kind with a phenolic insulator.  Strip out the center pin.  I bought a bunch of packages of phenolic-type RCA plugs from Radio Shack, and stripped out the center pins.  Leave the phenolic ring  insulator intact, as it makes a nice insulator.  They fit perfectly, and provide a neat solder point for the interface wires.

[N3DRB The Derb]

my HB used the 77 version. really nice iron. Match anything to anything just by arranging jumpers.

[k7yoo]

I pulled original pins out of the transformer and measured them:
.125" diameter X .5" long.
When you crush down the flex portion of a standard banana plug it is .125" in diameter. The small pins on a 1625 are also the correct size--trash a 1625 and break the base apart to get the pins. Ed has the right idea with the RCA plugs--break off the ground shell and you are there.
If you really have to have the originals I will pull them out of my transformer and send them to you.

Skip

[Todd, KA1KAQ]

Thanks guys -

No need for originals, Skip, but thanks for the offer. I'm mainly concerned with something that grips well once inserted. The small banana plugs slip in and out too easily. They don't have a lot of slop once installed, they just don't seem to grip. My concern is that straight/smooth pins can easily wiggle free or lose contact, causing big problems. So I'm curious to know how they held them in place beyond good ol' friction.

Sounds like a job for ducktape!

 

[k7yoo]

STANDARD  BANANA PLUGS--I THINK RADIO SCRAP MAY EVEN STILL HAVE THEM. THE MINI ONES LIKE USED AS PART OF THE ARC-5 CONNECTORS ARE TOO SMALL--AS YOU DISCOVERED.

[Todd, KA1KAQ]

Okay, Skip - I'll grab up some of the larger ones. I tried using an old test lead banana plug to check for size, but they seemed too big. I'll dig around and find some better ones. At least they won't fall out.

[Ed-VA3ES]

Todd, it seems your transformer has a different configuration than mine. Mine uses a smaller size pin, identical to the center pin of an RCA plug.  Yours appears to be bigger. That's where my confusion arose. 

[W9GT]

Hey Todd,

I have one of those transformers, as well (the 300 Watt variety).  I used regular size banana plugs, however, there is another possible source of the straight-type plugs that were originally used and look like big pin-plugs.  They are the plugs that were used on old Motorola two-way control head cables.  They were also used on the old (ancient ) Motorola 30D and 50B coffin box FM two-way stuff.  I used to have a lot of that stuff, but don't have any left.

73,  Jack, W9GT

[Todd, KA1KAQ]

Thanks Jack, Ed, Skip and everyone else. I didn't have a chance last night to investigate further, but when I tried regular banana plugs before, they were way too large. The smaller 'ARC-5' size fit the holes fine, no slop to speak of, but not what you'd call 'snug' either. They could fall out if bumped or jarred.

Part of the problem may be the year/style of my transformer and different pin sizes as a result. I know UTC changed the sizes and style of transformers like the VM-5 to CVM-5. My Multi-Match T11M78 has 6 or 8 ceramic/porcelain insulators on each end with holes in them for small pins. It's not one of the cube-shaped models with all the terminals on one side. Rectangular, two mounting slots on each end, and nice 'ears' along the top ends for carrying. 'Thordarson' tag screwed to the top center of the core, tag with model number is on the lower side.

While I can see the advantage of flexibility from being able to change jumper cables between terminals, I'm confused as to what keeps the plugs in place if they aren't a tight fit. I'm used to threaded studs or other ways of fastening such connections, and having never seen the correct pins or connector(if such a thing existed), I'm sounding like the dope I really am.

A picture or two, along with further measurements, is probably in order.