How to handle Reclaimed Transformers

[athos56]

So I got a PSU from an old Hammond Organ, It has 2 High Voltage windings, (2) 5v windings, (1) 6.3v winding, and a low voltage winding for a negative supply (It rectified to -24v). The Thing is Huge and came with 2 chokes that formed a choke input supplies for the High voltage winding.

Sooo, I stripped the chassis and plan on reusing it. My main question is how to best reclaim the transformers. Should I take the end bells off and replace the lead wires with new ones? Or just use the old wire? When I repaint it should I just leave the whole thing together, sand it down and repaint or take off the end bells and do them separately?

Any advice or best practices would be appreciated.

[Iain McNeill]

If you're going to use it in a high voltage design, I would test the isolation between windings to make sure the insulation hasn't broken down.

A "HyPot" or "Megger" tester is needed and these generally apply up to 1500VAC and measure leakage currents in the 100's of uA range. IIRC, 50uA is a pass/fail limit for 1500VAC for consumer gear. You crank up the voltage until the beeper tells you it's failed.

However, you do not want to test to failure because once you have punched a hole through the insulation with a discharge (spark) there is a low impedance path left by the carbon trail.

So test to the rated insulation withstand voltage specification only.

[HollowState]

Originally posted by athos56
Should I take the end bells off and replace the lead wires with new ones?

NO! You will almost surely find that the wires are anchored tightly underneath the coil build covering. This covering is probably varnished or impregnated with sealant and may also be stiff and difficult to work with unless your are very experienced. And there is little room inside the cover to do anything like splicing wires. The best thing to do is to extend the existing wires already outside of the housing using quality materials and spliceing procedures. A small double hook soldered splice covered with plastic tubing (or spaghetti) and covering that with heat-shrink tubing.

If possible, use the existing wires as they are. Of course this is assuming they are soft and pliable. Not hardened and dried out with cracking insulation. If this is the case, don't use it!

When I repaint it should I just leave the whole thing together, sand it down and repaint or take off the end bells and do them separately?

This mostly depends on how fussy you are and how much work you are willing to do. Personally I would prefer to refinish the covers seperately because it gives it a more professional appearance. But if you don't remove them, at least remove the bolts before painting. You'll get the same basic finished look that way.

edit: I'm also a traditionalist and prefer semi gloss black. Please, no candy-apple colors.

Victor

[athos56]

I tried to pop the endbells off, the top had a plastic cap through which a potting compound was poured. The top bell came off but the bottom seemed to want to stay put so it gets to stay. The wires seem ok.