The AM Forum

I got the r-392 up and running.  The problem was the IF (can) transformer had an open in it.  Fortunately there was a vfo section for sale on ebay at the same time and I replaced the transformer.  I figured the vfo had it's own problems since it wasn't paired with a receiver.  My question is on rewinding the original transformer.  It has hard resin or something coating the hole thing, is there a way to get this off?  Maybe it's more trouble then it's worth...

transformer is in the 3rd picture

and since everyone else is posting theirs....my link coupled tuner.

It is either coil varnish or ..........MFP

MFP is miserable to remove. Paint stripper will take it off but usually ruins everything around it.

Sometimes, MEK will soften that goop on those coils enough to get it unwound....I did it once..It took all day to get it unwound and rewound...and it worked, but what a chore......
   I like that link coupled tuner!...very buzzardly...Is that hot glue holding the coil spacings...?

I use hot glue for all kinds of radio projects.... Good luck with the coil....

What is MFP?  I did a google search and just got a bunch of rubbish about multi-function printers.  About as useless as the search feature on this BB.

Have you tried heating it?  Sometimes that stuff is just wax, which melts easily with a heat gun.  I'd try that first.  Rewinding that coil might be tricky, however, especially if they used some kind of special winding technique like a honeycomb coil. I think those R-390 (non-A) and 392 i.f. resonators are a lot more critical than were the more traditional Hammy Hambone and BCL i.f. cans.

It's probably varnish.  Try Denatured alcohol.  If that doesn't work Acetone would be the next stronger and then MEK, methyl ethyl ketone (avoid MEK fumes and getting on skin). 

Thing is, you want to dissolve the varnish on the coil bu t not dissolve the enamel insulation on the wire.

If the coil is crapped out anyway, it wouldn't matter.  All you want to do with the original coil is unwind it and count the turns and note the winding pattern, so you can duplicate it with fresh wire..

MFP   isn't that the fungus protection goop required by the gov't during WW2?? I have a couple Military rxers that have MFP applied stenciled on the back

Yeppir, that nasty yellow stuff.

With any luck the break will be at the solder connections or just under the coil gunk on the top layer. Wire corrosion from the solder flux is very common in small wire coils.

Carl

I have gotten lazy in the last few years and it's very rare, that I'll take the time to rewind anything. I'll keep my fingers crossed for a donor unit or an eBay item. Fair Radio has come to the rescue many times for coils in the RF deck of my 390A.
It has been very rare luck for me to find the fault as a bad solder joint at the terminal.......too easy.
The TUNER is very nice. That is a helluva vacuuuum variable and turns counter..........nice!!

   It is plastic spacers I can't remember what the purpose for them is but they work great for winding coils.  I did use hot glue to secure the copper to them.  I will try the techniques posted starting with heat I guess and see if I can maybe repair it.  I don't want to turn it into a major project in itself if it's going to be to much.  If I can fix it I'd like to though because I would have another spare and save a part.  On the tuner it is a Russian vacuum variable.  It's way over kill but it's just sitting around right and figured I would put it to some sorta use.  One of these days maybe I will collect enough junk to build 2x813 driving 2x813 and it won't be so much over kill anymore.  At Belton next month maybe I'll finally find a plate transformer

MFP stands for Moisture and Fungus Protection. It was sprayed on to a lot of WWII surplus gear I bought from Fair Radio way before I was a ham. Usually on the underside of the chassis, completely soaking the wiring harness and covering all components.

Has a yellowish appearance, and a simply heavenly smell that brings back fond memories. :-)

OK Fine!!!
Those Ruskie Vac variables are beauties........I bought one recently to fix an antenna problem......nice!!