TAD 150 Pre Amp transformer died

No need to sell for parts any good repair place will simply replace the tranny with one spec'd accordingly.

What area to do live? Goodness even I could do this simple job. You can get your pre fixed for sure.

I'm in Tampa. The stereo repair shop I took it to
couldn't find anyone that could make a replacement (≤$400 anyway),
as the machinery to make toroid transformers is apparantly very expensive.

As it stands the only option is to send the blown transformer to
Mercury Magnetics and hope they can make a comparable CI version.

But I'm happy to pay you, Grannyring, if you can do it.

Take Grannyring's advice, The 150 is an excellent pre and you should Be Able to find a competent repair shop to do the work

Hope you're right, but the search has been nothing but discouraging so far.

Here's the reply from Hammond Mfg:
"Sorry but that would be a custom design very expensive to do but before you ask for a cost I need the amperage for each output voltage."

Is that even possible to calculate from a dead transformer ?

Maybe Tube De Force in Canada can assist you.
tubedeforce.com
They do a lot of rebuilding and ressurecting of old amps and improve on the original as well as consult on some very large scale projects.

All the best,
Nonoise