No short w/ bulb, short w/o bulb

[lowell]

Got an old Challenger CA Danelectro amp on the bench. Plugged into my bulb limiter the bulb is dead, no glow at all. Plugging the amp into the outlet blew the circuit breaker instantly. Never run across this issue before. Quite odd. Any clue as to how, or why, this would be happening? Btw the tubes do glow when plugged into the limiter.

[lowell]

Also measured resistance across power cord plug. Getting 4ohms to earth from one pin and 1ohm to earth from other pin. Something tells me the primary of the PT is shorted. But why wouldn't the bulb show this?

[52 Bill]

Also measured resistance across power cord plug. Getting 4ohms to earth from one pin and 1ohm to earth from other pin. Something tells me the primary of the PT is shorted. But why wouldn't the bulb show this?

Check to see if there is a short in the primary wiring to the ground, either in the wiring or the transfrormer itself. I assume that the amp has a two wire power cord.

[J M Fahey]

You should have no continuity *at all* from any pt primary leg to ground.