Bob,
I think you have the right idea. Bring it up with the Variac without
the rectifier and see if everything lights up, and then start over with
the rectifier in place.

I would keep a voltmeter on the B+ line as you bring it up.

I had an HX-50 in my shop almost 30 years ago, and remember the rig but
don't remember details.

Recall that it was a filter type SSB job with a 6DQ5 final and put out
maybe 30-50 watts or so.

Do you have any history of the rig and did it work before the
transformer conked out?

John