Judge a OPT by it's cover?

linuxslate

Well-Known Member
Someone local is selling an A-4359 Jukebox amplifier. This amplifier uses 7868's, which apparently are electrically very similar to 7591's, but a different base.

I was originally thinking of purchasing the A-4359, and basically "bashing" it with my rebuilt 7591 Lowery Organ amp resulting in a "frankinamp" with the OPT's of the A-4359, and most of the rest of the Lowery Tube amp.

But now I am thinking of just using the iron from the A-4359, to build a new amp. Obviously, I am going for a very low-budget build here. The goal would not be sound or beauty. I'd basically be saving the iron, and learning from my first real build.

Now the problem/question: The A-4359 jukebox amp is in very poor condition. The chassis, and all transformers show significant surface rust. It is un-restored in anyway. I'd be scared to plug it in even if I had a Variac that went to the millivolts.

Given the poor cosmetic condition of the OPT's, what is the consensus that they would still be in functional and safe condition?

Of course I'd do winding continuity and winding-to-frame short checks before I did anything else. I figure I could also use another amp's B+ to do an informal HiPot of the OPT's. (Frame and appropriate secondary tap grounded).

If they pass the above tests, and I can easily remove surface rust, are they probably magnetically OK? Can rust get in between the laminations, and magnetically short them out? Any (reasonable) way to test?

If the OPT's are not good, I'll salvage parts, and bin the rest.
 
Unless they've been soaked in water they are probably fine. Ohm them for shorts to case and opens, and if it makes you feel better bake them at ~150 for a while to drive out any excess moisture before adding high voltage.
 
I have a Rowe R-4359 but haven't done anything with it so far. An interesting idea that you might consider is that the OPT's have a 70V CT'ed winding that could be used as a cathode feedback winding.
 
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