Squashed profile toroidal to get in a 1U case of a 1992, Ampeg B1 amp,
export version, internally set for 240 V use, blew (violently) the mains
fuse. No burnt smell or obvious damage to the transformer.
Disconnected and removed there are 2 seaparate primaries , 1000 Meg , 500
volt isolation between them and the secondaries.
3 wires to each primary , presumably 110V and 120 V each pair. Measures
about 3 ohm over each "120V " pair of separate primaries which seems about
right for a good 450 VA transformer.
Connect either primary to a 20 volt ac variac supply and they draw 1 amp of
current. I could understand a failure in one primary but both failed the
same ? Could there be failed VDRs or something buried inside the transformer
?