The AM Forum

Hi.  A boatanchor transmitter from the late 1950's (that I am considering purchasing) has rust on the power and modulation transformers.  It looks superficial, and there are no other signs of neglect or abuse.  Is rust pretty standard on these?  Is it indicative of serious problems?
Thanks and 73
Steve

Yes.

No.

Repair consists of spraying black paint in a rag and rubbing it into the laminations to make it all nice and shiny again.

73 John

how about that stuff in a spray can that turns rust black??
I bought some at home depot a while ago.

Rust indicates some level of dampness was involved. I'd bake the transformers for 6-8 hours before painting, just to be safe.

On questionable looking transformers, I pull the end covers off and bake them in a toaster oven for 6 - 8 hours at 180 - 190 degrees, then pull them out of the oven while still hot and drop them into a bucket of oil-based varnish to cool. After they cool down in the varnish, I pull them out and let them drip dry. When cooled to room temp, I dunk them a few more times and let them dry between dunkings. This leaves a nice varnish glaze on them. Let them finish drying for a few weeks and reassemble them. this will usually give an old nasty looking transformer a new lease on life.
                                            the Slab Bacon

I like to use a little shoe polish on the lam ends.....The oil in the stuff, allong w/ the rubbing makes it look OK in a flatish way..  cheep, dirty and quick.....   klc

Actually, better than baking for just a few hours is to leave the xfmr in a dry, heated room over the winter, for several weeks or preferably, months.  It's kind of like letting wood season.  It took the transformer a long time to soak up the moisture, so it should be given a long time to dry out.

Mike, NI4N, (now W4AAE) picked up an open-frame kw modulation transformer that had been stored in an unheated outdoor shed for several decades.  He cleaned off the rust, and checked it out with his hi-potter.  The leakage currents between windings and to the iron core were so high that he thought the transformer was beyond salvage, but he left it sitting in his heated basement all winter, and hi-potted it again after several months.  The leakage current was near zero, comparable to what a new transformer would be!  He put it in a rig with a pair of 833A's modulating another pair, and it was still working perfectly when he sold the rig.

If you do put the transformer in an oven, don't run the temperature too high.  With an older unit, I'm not sure I would even risk 180 degrees.  I would keep it more like 140 degrees F.  Even in the oven, I would let it bake for a week or more at that temperature - the longer the better.

An electric oven is preferable to a gas oven for this purpose, since water vapor is a by-product of the combustion process with natural gas or propane.