Well, after melting the power transformer on my preamp, I found... nothing wrong. I mean it might have been a transient short from something mechanical I did, but all the electronics on the secondaries seem ok and drawing current within the transformer's spec.
Anyway I replaced it and added a fuse on the primary, (the original vendor left it unfused), so we'll see what happens.
The next step is to see if I can fit a voltage regulator board in that case (oh, and to build that board).