[Greg]

I looked at the battery eliminator guy's transformers. The core-less ones are too small. I need 1"x1" and his are 3/4". I suppose it's possible I could fit an entire transformer into the old housing.

Next I let myself get talked into rebuilding the original. I ordered wire and did some calculations based on the bobbin size, wire gauges, primary resistance ... It's a lot of wire, but not impossible. So I ordered the wire.

The transformer wire wire arrived. The following day something motivated me to look on Ebay for a replacement (didn't find one earlier). There can't be too many of them out there. Sure enough I found one. So I bought it. Looked new.

I got it today and it sure looks new. However the primary resistance sure doesn't read like new. It's better than the original (primary open) but reads ~5.5K ohms instead of the specified 420 ohms. That can't be good.

Is there some failure mode on these that affects the primary? The only thing I can think of is the wire corrodes at some point and it goes open or the resistance increases as in the case of the second one.

Better start thinking about winding...