TAD 150 Pre Amp transformer died

Try Mercury Magnetics. If they're still around, they used to rebuild transformers or might have a matching replacement.

That preamp as well as TAD amps were made my a Chinese company called BEZ. Paul of TAD would then finished them out with some finishing steps.....

The transformer is most likely a BEZ and they still are in business and sell transformers. I bet you can take the old one out, take a picture and jot down the specs, then email BEZ for a replacement. I heavily modified a TAD 60 and have emailed BEZ thus this knowledge.

http://www.bezdz.com/engindex.html

The Tad 150 was made by a Chinese company called Audcom. I believe Bez made the amps for Paul