Replacing Tattered Cloth Leads On An Old OT

[rp]

On this old Stancor from my other post the cloth is falling apart, right at the bells too. I really hate the shrink tube over the old leads look. I intend to cut the leads off inside the bell and solder on new lengths and shrink and also bury the unneeded taps in the bells.

Any reason not to do this? Any tips before I do? When I splice I usually parallel 1/2" of the two leads and 'wire wrap' them together with something like a 32AWG strand pulled out of some scrap wire, then solder, then shrink.

Any issues with rattles, or fields and hum with the unused buried taps i should be aware of?

What gauge is fine with a 35-50W OT? I ask since the secs here are pretty heavy solid core but I've seen 100Wers with just 20 AWG on them. I might use cloth and I only have 20AWG.

Purely aesthetic poll: Go with cloth or PVC? I like to respect old things, but I'd have to order 3 more rolls of cloth wire and that's $40 with ship, and I never use the stuff. A lot of money for a few feet just to treat and old tranny right. If anyone has 6 16" lengths of 6 different color cloth hook-up to sell me reasonably I'll paypal you most happily.

Also, this OT looks lovely as it is I wouldn't paint it, but there are a few chips on the lams with rust. Leave alone or touch them up? And if the later with what? Is rust killer paint safe here?

[Phil_S]

I intend to cut the leads off inside the bell and solder on new lengths and shrink and also bury the unneeded taps in the bells.

Any reason not to do this? Any tips before I do? When I splice I usually parallel 1/2" of the two leads and 'wire wrap' them together with something like a 32AWG strand pulled out of some scrap wire, then solder, then shrink.

I've done some transformer repair work. There is no margin for an oops, particularly when you are in the space between the bell and the winding wire.

I would not focus on any cosmetic consideration. If you have to go down to where the wire from the winding meets the external lead, I promise it will be trouble and you'll sweat it. This is a fairly valuable OT and what's most important is to have it functional.

Here's what I would do, and this has some hindsight wisdom to it. I would pull of the end bells and slip some heat shrink down the lead to insulate what you will be leaving untouched inside the end bell housing. This is to reinforce and re-insulate what is already there. If the outer cloth is in poor shape, carefully remove it, but don't employ any sort of sharp tool that might nick the wire. Often there is a second layer of something under the cloth. If the second layer is brittle and cracking, remove that, but try to leave at least a little bit that you will sleeve with heat shrink. Don't open the paper and don't mess with where the old lead is soldered to the winding wire (trouble lurks there).

Now, strip off all the remaining insulation above the 1.5-2" or so of heat shrink that stays inside the end bell housing. Don't make that 1.5-2" too short and leave yourself extra to cover for a mistake. You'll be able to figure a way to put all of that inside. You'll be cutting most of that away, but don't hurry to cut. Employ the carpenter's rule, measure twice, cut once. It's even worse here because you can't just get a new piece of wood.

Now, make a proper splice, new lead to old lead. The Western Union splice is probably the best one. Use the internet to look for the proper way to splice wire. No shortcuts here. I don't like butt connectors because they are bulky. Even so, the spliced area isn't flexible and you want to figure just the right place to place it so that the splice can also be hidden inside the end bell. You'll want to cover it with heat shrink, too. I would not wrap the splice, as it will be much too bulky.

You will find the space inside the end bell getting crowded. You may need to compromise and make the splices outside, so evaluate the whole job very carefully and make sure you can finish it OK. Have a clear plan to get from beginning to end and follow the plan. Take digital pictures along the way -- these are just in case you aren't sure what something looked like when you started and you need a reference. Short term memory is shorter than you think.

Because this is work that you do not ever want to do over (the reasons will be even more obvious when you are doing the work), I'd use the best quality wire I could find. On a 50W OT, you should have 18 AWG wire. Check what's there -- you can use whatever it came with. I would choose PFTE wire, and I'd make the leads at least 6-9" long.

Any issues with rattles, or fields and hum with the unused buried taps i should be aware of?

I don't think so.

What gauge is fine with a 35-50W OT? I ask since the secs here are pretty heavy solid core but I've seen 100Wers with just 20 AWG on them. I might use cloth and I only have 20AWG.

If you must, 20 AWG is probably OK, especially if it is what is already there.

Purely aesthetic poll: Go with cloth or PVC? I like to respect old things, but I'd have to order 3 more rolls of cloth wire and that's $40 with ship, and I never use the stuff. A lot of money for a few feet just to treat and old tranny right. If anyone has 6 16" lengths of 6 different color cloth hook-up to sell me reasonably I'll paypal you most happily.

I've already made a recommendation against this in the strongest terms. Cosmetics are not important unless you are restoring this for a collector, in which case you need to go down to where the lead meets the winding and where I have already promised that you'll find trouble.

The "trouble" is that the winding wire is very fine and coated with varnish. You've got to remove the varnish to solder to it. Because it is so fine, it breaks very easily. In no time at all you'll find that you used up the length that was outside the paper and then you are forced to dig deeper. As it gets worse, you'll be left with no alternative but to split off the lams and remove the core. If you have never been there, and you are the least bit unlucky, you will learn quickly what the inside of a transformer looks like and repairing it will take you days or weeks.

IMO, this trumps any consideration of respect for old things and whatnot. It is a worthy thought, but impractical unless you really do know what you are doing and have the experience to pull it off with no margin for error.

Also, this OT looks lovely as it is I wouldn't paint it, but there are a few chips on the lams with rust. Leave alone or touch them up? And if the later with what? Is rust killer paint safe here?

A few dabs of Rustoleum won't hurt, but I wouldn't paint it. Make sure that paint is good and hard before you attempt to handle it, or you'll have a mess.

Good luck.

[Cliff Schecht]

That is all great advice. I've rescued my fair share of vintage transformers and have never had to actually desolder wire from under the paper to repair a unit. Well I did once on an old Gibson amp to recover a reverb transformer but this fix lasted all of 10 minutes and is not recommendable unless you are really good (i.e. practice on junk before ruining your irreplaceable iron).

Small rust patches are no big deal. Heck even large amounts of rust isn't a big deal unless it starts splitting the laminates or something.

I've found that the wire INSIDE the bell covers is almost always recoverable, if not in perfect condition. This is where humidity has had the least chance to do its damage. I'll usually try to recover as much of the original wire as possible and tack onto this, that way you don't have a bunch of heatshrink bunching up at the bell cover opening. The unit you posted in the other thread is in fine shape, you should be able to recover the wire no problem.

[rp]

Phil - fantastic info, glad I asked first. I step lightly into the unknown but I was never sure what was inside trannies. So it is thin magnet wire? I will be very careful at the joints with will not muscle the wires around too much. The WE splice worries me at the 20awg solid cores at the secs especially the doubled up 4 ohm tap. I will have to ponder this one.

Cliff, Phil scared me a bit, you reassured me - Off I go. Maybe I'll post pics if comes out nice for future reference.

BTW I have exactly 6, ~16" lengths of 18 awg teflon in the whole house. Red white blue and black green yellow - I'd say it's destiny, but I really hate the new on old look - I must think on that too.

[Cliff Schecht]

I'd recommend you shy away from the Teflon stuff for these types of repairs. The Teflon wire is by far stronger than the cloth covered stuff and is much heavier to boot. The transformer wires are around 20-22 AWG for older Stancor stuff IIRC and this doesn't hold up so well against the Teflon wire. Worst case scenario is the transformer wire breaks right before the solder joint or you move the wires around too much trying to flex the Teflon around and break the original wires inside the transformer. You want to support the leads without putting unnecessary strain on them. I use zip-ties to clean everything up and take the weight off of the tranny wires, especially if the iron I'm using is ancient and unknown.

[rp]

I'd recommend you shy away from the Teflon stuff for these types of repairs. The Teflon wire is by far stronger than the cloth covered stuff and is much heavier to boot.

This occurred to me. I prefer working w/ teflon but it get's to be a PITA above 20 awg. PVC won't be so discordant looking either. If you got a '50s car you should put whitewalls on it.

[Phil_S]

I think that Ciff has done a bit more of this than I have and suggest that taking his advice over mine, in case of a conflict, is the best course of action.

One thing we both seem to agree on in spades is that you don't want to get down to where the original leads meet the winding wire as you have zero margin of error in reworking that, and surely, whatever you do will lead to trouble, with a capital T.

Considering that Cliff thinks that you probably have a good deal of recoverable wire, I am reconsidering what I said in a number of areas.

First, you can probably get by with something other than the WU splice. What you should not do is lay the wires parallel and make a solder bridge to join them. What I think you describe is little more than that -- parallel wires with a bit of wire wrapped around. There is not mechanical connection there.

The splice needs to be a good mechanical joint and solder is meant only to hold it together. In other words, don't depend on the solder to complete the splice. I sometimes make two hooks and loop them together, twist above the loops, and then solder. Over this goes heat shrink. It is still bulky and it is not flexible. If you can do this outside the end bell, I think you will be better off. If you are working close to the bell, you might be able to slip the h/s tube down into the bell, but the hole where the wires emerge will start to get very tight. Considering what Cliff says about wiring inside the bell, I would probably inspect it to be sure and then close it up. See if you can keep all the work outside the end bell.

If you keep it all outside, then I think your idea of using vintage cloth wire or anything else you like is going to be fine, as long as the rating on the wire is appropriate to the voltage. Much commonly found wire is rated for 300V and this is probably fine for everything but the primary wires. If I recall, this OT is intended for 6L6 or EL34 on the primary side and you are likely to run up well above 300V, so, for that, you'll need 600V rated wire. On account of this, I'd probably use 600V wire everywhere, just to keep myself from making an unintended error.

The danger with the voltage rating of the wire is that the rating indicates the point at which you should expect the insulation to fail. Inside, the copper is pretty much the same stuff -- it probably varies a bit from maker to maker, but the differences are inconsequential for what we do.

You've got a nice OT there. Careful with what you do. I'm sure you'll be able to get a good result. I didn't mean to scare you, though the warnings were to keep you from getting the better of yourself and it seems that worked!

Regards,
Phil

[Cliff Schecht]

The cloth covered wire they used in really old transformers is of pretty small diameter. It worried me on my first build or two (both used ancient iron from the 50's and 40's) but eventually I got used to the fact that this is how they used to build these things and I haven't ever actually had a problem with older units shorting out. Of course when in doubt I test on a function generator and then a variac only if the first test checks out alright.

I've gotten away with using some pretty pathetic looking transformers (rusty, short wires, etc..) by doing the least amount possible that I needed to to ensure safe operation. Just about any wire repair or lengthening operation can be made by stripping back about 3/8" of insulation on each wire and twisting the ends together securely. Solder it, heatshrink it once or twice and give it a tug to check the joint strength. It just needs to be strong enough to not break under vibration, in a properly built amp the lead should never be under enough stress that it can be pulled apart. I'll add flux if the old wire is oxidized (green) and use two pieces of heatshrink if I have room for added peace of mind.

Rust doesn't hurt anything unless it is physically deforming the transformer or has rusted through the laminates. Any good quality old transformer that was treated even decently should be usable. Anything near oceans, etc I would expect to be rusty just from the salt in the air but probably still usable. I haven't had a single transformer fail after running the few simple tests I do (ohm it out, function generator and scope for OT and PT, variac if PT).

[rp]

One thing we both seem to agree on in spades is that you don't want to get down to where the original leads meet the winding wire as you have zero margin of error in reworking that, and surely, whatever you do will lead to trouble, with a capital T.

I will steer well clear. Next junk tranny I get I'm gonna tear it apart to get a better feel for these things.

I sometimes make two hooks and loop them together, twist above the loops, and then solder. Over this goes heat shrink. It is still bulky and it is not flexible. If you can do this outside the end bell, I think you will be better off. If you are working close to the bell, you might be able to slip the h/s tube down into the bell, but the hole where the wires emerge will start to get very tight. Considering what Cliff says about wiring inside the bell, I would probably inspect it to be sure and then close it up. See if you can keep all the work outside the end bell.

I do the hook thing too when there's no other choice because of the bulge. If it fits in the bell that's an option. It's only on the thick solid core secs that I'll have a problem. I don't want to twist them as they'll likely torque back to the joint at the wind. I don't even want to bend a hook on them. How about the joint in the image? I do this often when I need a joint with a profile no larger than the original wire. Yes it might pull apart but once soldered you'd have to pull so hard the connection at the coil will probably go first. I don't think you can pull it apart by hand either. I just worry it's a valid electrical connection but the wire-wrap people do this.

If you keep it all outside, then I think your idea of using vintage cloth wire or anything else you like is going to be fine, as long as the rating on the wire is appropriate to the voltage. Much commonly found wire is rated for 300V and this is probably fine for everything but the primary wires. If I recall, this OT is intended for 6L6 or EL34 on the primary side and you are likely to run up well above 300V, so, for that, you'll need 600V rated wire. On account of this, I'd probably use 600V wire everywhere, just to keep myself from making an unintended error.

They have to be inside as the cloth is shot right where it exits the bell. Didn't think about the 600V rating - I'm screwed, I've nothing around in 18awg. Gotta find someone that sells wire by the foot, 3 100' spools of 18awg are gonna cost me more than the tranny! Maybe time to dumpster dive.

[jborders5]

They have to be inside as the cloth is shot right where it exits the bell. Didn't think about the 600V rating - I'm screwed, I've nothing around in 18awg. Gotta find someone that sells wire by the foot, 3 100' spools of 18awg are gonna cost me more than the tranny! Maybe time to dumpster dive.

How much do you need? I have two end spools of Belden 8522 18 AWG rated to 1KV max. I'll gladly send you a few feet of each. One spool is white/red & the other is white/brown, so it shouldn't be too difficult marking them. I also have lots of 300V in different colors that should work on the lower voltage windings.

[Phil_S]

That picture is exactly as I imagined what you described previously. I'm no expert, but it is my understanding what you are doing there does not qualify as a proper splice. You have two parallel wires there and you are using a solder bridge to connect them. The outside wrapper, in my view, does nothing to make a proper mechanical connection. You'd be better off using butt connectors. So go the the Home Despot an buy your self a small box of the uninsulated kind, which you can cover with heat shrink so they won't be so bulky. You can even cut them in half with a hack saw and then what you crimp down on the strands will be very small.

Anyone have another take on this?

I don't have very much 18 AWG 600V at the moment, but I'd be happy to send you some adequate sized scraps of yellow and gray PVC covered, and I've got a little bit of green teflon covered in #18. I used to have some orange, too, but didn't see any in the wire box. Send me a PM here with your name and address. I'll put it in an envelope PDQ and mail it to you. I assume your are in the USA. Foreign post, all bets are off.

Phil

[Cliff Schecht]

EEK! I absolutely hate it when I open a piece of electronics gear and find crimp joints and/or wing nuts. Please do not go this route. I think Phil is overthinking the solder joints you'll need to make. He's right that you shouldn't just stick them end-to-end and solder though, you need to twist those strands together. I like to get a good 3-4 twists minimum before applying solder but I've never had one of these joints break on me after heatshrinking. TBH, I think your wire-wrap method would work as well. The solder isn't going to shear, that connection does have some physical support and would last I would think. Try this: Twist the wires, then wrap them .

[dynaman]

Dude, I've done this about a hundred times and haven't had a prob yet.

Yank the 'bells and save the fish paper.

Do you like red? Paint the endbells red. Or just leave 'em rusty and crusty. Nevr-Dull works GREAT for cleaning crud and oxidation, and it also leaves old paint shiny after it's been rubbed off with a cloth.

Trim the leads, leaving 1-2 inches. Some folks like to use a particular splicing method. I prefer to tin and make hooks on the existing and new leads (If you don't want to mess with oddball UL, 25V, 100V, etc. leads, then cut them short and cover with heatshrink).

Hook, squeeze and solder. Cover the joints and old insulation with 1 or 2 layers of heat shrink tubing.

If you don't like the appearance of your laminations, now would be a good time to lightly clean them them with an abrasive pad. Paint or clearcoat the lams. Or just rub them down with a Sharpie or paintstick. Or use shellac or varnish. Or "wet" them with a bit of Nevr-Dull. Or leave 'em alone. Do whatever you think looks cool.

Reinstall the paper and endbells.

FWIW, I don't care enough to get worked up about specific types of wire, so long as the insulation is good for 600V. I use stranded 20ga with teflon insulation.....because that's what I have. Sometimes I use PVC stuff just to use up some scraps.

[rp]

Thought I'd follow up, and leave a document for anyone in the future. Was easy, plenty of room in the bells, and the leads and casing were sound where they were protected inside the bells too. Still wish I knew why Stancor chose to use stiff solid core on the C/4/8?

One last question if anyone tried or knows: why do old leads always look lacquered or waxed? Is this just age or is it ok to give the new leads a coat of thinned amber shellac? Fire hazard? Will it make the leads crumbly and too stiff?

Hope it works when hooked up. Thanks to all for the help.

[rp]

Oh yeah, hats off to Radio Daze. I emailed explaining I just need 6 16" lengths of cloth wire for a small restoration and they helped out right away even though they don't sell by the foot. Terrific company!

-rp