A-431 OPT's Refurbished

[ChrisK]

OK, it's time to post some information about my Mark III stereo amp project. It's moving ahead on several fronts, depending pretty much on my moods:

The A-431 OPT's needed some TLC. Here's a picture of the original. Note the exposed lams and windings...Huh. What happened to the original potting material? The covers were clean, nothing melted.



The cooker: A metal can with a 100w bulb heats it up to about 180F in a couple of hours. Moisture is driven out and the core temp is ready for potting. Wires have been replaced, fish-papered and taped:



High-Tech potting station: Hot plate used to heat microcrystalline wax, the same substance used by the original AcroSound and Dynaco manufacturer. When heated to 180F, it turns into a liquid similar to the consistency of paint thinner and penetrates much, much better than varnish. No need for vacuum pumps etc.



One down, one to go:



All resistance values were checked before and after to make sure nothing got broken. Good so far. Next post: Chassis and Poseidon boards.

Chris

[Vince]

Nice work Chris!!!! Who was your wax supplier? Vince

[ChrisK]

Nice work Chris!!!! Who was your wax supplier? Vince

Thanks, Vince.

Apparently, the wax is still widely used by sculptors. Any good art supply store should stock it. I found mine locally at this place in SoCal, but they also accept internet orders:

http://op3.triadinet.com/artsupply/nlcatalog.asp, type the search term "microcrystalline" into the search box and you should find it. One or two pounds ($9 each) should be plenty for a couple of OPT's).

Be sure it's "microcrystalline" and nothing else. It's refined to an industry standard and has the highest melting point (180F). There's more info here:

http://www.fao.org/docrep/W6355E/w6355e0m.htm

Let me know if you need more info...

Chris