How do I correctly repair my UTC CVM-4?

[w1vtp]

I got this really nice UTC CMV-4 at the last NearFest (was really excited about the find).  However, I have a bit of a repair problem.  My first reaction was to just reattach the broken Bakelite using regular epoxy but Tim HLR cautioned me about the epoxy not handling the heat from a slobbering iron -- good point.

So the question is what's the best approach, product etc.  I've included a photo of the poor beastie.  The broken piece of Bakelite is resting against one of the posts -- not obvious.

Then there's the question on how best to remove those HUGE wires that are on the terminals without repeating the problem

73, Al VTP

[Pete, WA2CWA]

Heak sink the terminal before you apply the soldering iron to the terminal. Epoxy or super type glue will work on the bakelite.

[Jim, W5JO]

Regular set JB Weld, not the quick set type.

[k4kyv]

The wire remnants in the terminal lugs should unsolder easily enough.  Looks like the damage was done while the heavy wire was still soldered to the lug intact.  I have repaired the bakelite terminal boards of UTC transformers with epoxy with no problem.  I  would trust it over super glue.  I have found that bakelite repaired with epoxy is just as strong as the original.  Heat from soldering to the terminal lug hot enough to damage the epoxy repair would likely damage the undamaged bakelite just as much.  I am always sparing with heat to those transformer terminals.  Usually, tar oozes out around the terminal before any damage is done to the board.

As for the wire, it should be easy enough to solder the leads in place, whether with stranded or solid wire, in a manner that would not unduly stress the terminal lugs.  It looks like whoever wired that transformer didn't follow basic precautions with the mechanics of assembly.

[w1vtp]

Regular set JB Weld, not the quick set type.

JB Weld?  I am guessing it is available at hardware stores.  I'll check it out

73, AL

[w1vtp]

The wire remnants in the terminal lugs should unsolder easily enough.  Looks like the damage was done while the heavy wire was still soldered to the lug intact.  I have repaired the bakelite terminal boards of UTC transformers with epoxy with no problem.  I  would trust it over super glue.  I have found that bakelite repaired with epoxy is just as strong as the original.  Heat from soldering to the terminal lug hot enough to damage the epoxy repair would likely damage the undamaged bakelite just as much.  I am always sparing with heat to those transformer terminals.  Usually, tar oozes out around the terminal before any damage is done to the board.

As for the wire, it should be easy enough to solder the leads in place, whether with stranded or solid wire, in a manner that would not unduly stress the terminal lugs.  It looks like whoever wired that transformer didn't follow basic precautions with the mechanics of assembly.

Agree.  One option would be just to clean everything up with a solvent and then using a really old fashioned 150 watt iron with a liberally tinned tip go in quick and melt the slobber.  Then quickly suck out the slobber with and equally old slobber sucker.  I might come up with a special heat sink to grasp the bottom of the terminal to minimize and heat on the xfmr lead to the terminal.  I think the trick is get in and out quickly with no yanking or twisting.

73  AL

[Jim, W5JO]

Regular set JB Weld, not the quick set type.

JB Weld?  I am guessing it is available at hardware stores.  I'll check it out

73, AL

where I live JB Weld is available at most any store, even grocery stores, that sell automotive parts.  Check with auto parts stores, hardware store and Wal-Mart.  Just be sure to get the regular, not the quick set type.  If you don't find it, let me know by private message and I will send you some. 

It is a two part product that, when set, you can drill or file.  Be sure all surfaces are clean before applying.

[Ed-VA3ES]

Regular J-B Weld is a great product and handles very high temperatures well. 

[k4kyv]

JB Weld is regular epoxy with fillers added.  One tube comes in black, the other in white.  Mix them together, and it turns out dark grey, maybe close to the "St James Grey" made famous by Collins.  It is easy to tell if it is mixed uniformly by looking at the texture.  It is supposed to withstand several hundred degrees F, and is recommend for such applications as engine blocks.

I have used regular clear epoxy, the slow kind, to cement loose plate and grid caps back on to transmitting tubes.  It turned opaque black after a time, but seemed to still be mechanically solid.

[Bacon, WA3WDR]

There is a blue epoxy that I have used that is very hard, and very resistant to heat.  I used it as a thermal coating on PC boards, and unfortunately I had to remove a defective surface mount capacitor from beneath it once... and it was very hard to do!  The stuff was so hard and so resistant to heat that it was quite a struggle... it's tough.

It's expensive, though, so it may have limited application in amateur work.

This epoxy comes in a mixing bag, so you have to use the entire package at one time.  As I recall, it takes about an hour to stiffen up, and it hardens overnight.  I see that the description says 90 minutes to start, and 24 hours to harden.

   Bacon, WA3WDR

----------

Heat-Conductive Insulating Epoxy
 
This smooth paste conducts heat, maintains electrical insulation, and is ideal for attaching transistors, diodes, resistors, and other heat-sensitive components to printed circuit boards. Resists salt solutions, mild acids, and alkalies. Bonds some metals (including steel, stainless steel, aluminum, brass, bronze, and copper), silica, sapphire, ceramics, glass, fiberglass (FRP), and some plastics (including ABS, acrylic, and polycarbonate). Comes in a dual-pouch packet with resin and hardener already measured. To use, remove the clip separating resin and hardener, mix contents inside, and dispense. Color is blue. Temp. range is -94° to +239°  F. Thermal conductivity is 10 Btu-in./ft.2 -hr.-°  F. Its ability to withstand electrical voltage without rupture is 410 volts/mil. 

Begins to Harden: 90 min.
Reaches Full Strength: 24 hrs.
Size 1.4 oz.
McMaster-Carr # 66395A11
Each $14.34
 
 

[Opcom]

All the comments are on target from my experience fixing similar components.

If you are not extremely concerned about cosmetics of the underside of the unit, just make sure none of the electricals are touching or too close, and either put JB weld or epoxy in there, and then stick the broken pieces back on, assuming they can be fitted back into place. If you have some potting compund which is thin when mixed, you can pour a little in there to give a smooth appearance to the base of the unit. I've used JBweld to fix many bakelite/plastic/wood/glass/metal items. At one time I thought it had metal filler and would conduct, but I have not had any problem with a broken insulator on a choke where there is 2500V to GND. Unknown the extreme hi-pot characteristics of JBweld.

I myself would eschew that final cosmetic step, and just go for an electrically and mechanically sound repair. To me, it's the functional nether side of a transformer only rarely seen, not the dashboard of a restored 1957 buick electra. Of course, I never naysay anyone wanting a perfect restoration that will stand up to the inspection of Collins Collectors and I enjoy seeing other people's beautiful work.

Please make pictures and notes as you fix it, and post them on the internet as a little article! I did these on a small air-variable (60VDC+144MHz grid drive to a 6146) and a busted-up variac, and others found them useful.
http://www.bunkerofdoom.com/cap/fix1/index.html
http://www.bunkerofdoom.com/adjavolt/index.html

An important part of our hobbies is to show exactly how we repaired irreplaceable items. Such skills and articles are today unique to groups like ours, but were common in previous generations.

Just my 2 cents!