Thomas Day's Comments

Look for a current drain.

My first AW-23 had a shorted primary when I acquired it 15 years ago. (I should have been suspicious of the 10 amp primary fuse  ...  like maybe a proper 3 amp fuse would blow.). Anyway, I recapped it before powering up the first time on my variac. The proper size fuse  would blow when my variac reached about 40 volts. I eventually obtained another power transformer from a rough amp, and the radio ran great. Then a year or so later the fuse blew Christmas day, after it had been playing 3-4 hours ..... same problem as before, blowing the fuse at moderate variac voltage.

The ultimate problem turned out to be in the speaker. The red B+ wire inside the pedestal from the speaker terminal strip to the field coil was laying across the point of a screw and made a partial connection at high voltage through the worn insulation. Excessive current was not quite enough to blow the fuse but enough to overheat the transformer,  progressively cooking  the transformer until the primary failed blowing the fuse the day I ran it several hours. I found the problem by close visual inspection of the routing of the wires in the speaker. Corrected the wire location, and the power transformer #3 has worked out fine for many years.