Bad Power Transformer?

[Daver]

I'm pretty sure I have a bad power transformer on the Ampeg B15 flip top I'm working on. It was replaced sometime in its life with an old Thordarson. The owner got it from some estate sale and said it was working briefly until it started smoking. It never blew the fuse. I tested all the tubes and made a visual inspection and checked connections to ensure there were no shorts to ground before bringing it up on a variac. While doing so, when the DC output got to around 175v, it started making sizzling and popping noises coming from the PT. I stopped there and let it cook a bit. After about 5 minutes the PT was starting to get warm. Any other tests I should do before pronouncing it dead? Thanks.
Dave

[txstrat]

Have you checked if the fuses have the correct value? Maybe there was a short and the fuse(s) should have blown.
Sizzling and popping along with smoke (like the owner said) I'd also pronounce it dead.

[Daver]

The fuse that's in there now is the correct value. I can't say 100% it was always that way, but apparently the current owner had not changed it. Thanks!
Dave

[Enzo]

Disconnect the secondaries and power it up. Does the transformer still get hot and bubble? If so, say goodbye to it.

[txstrat]

Enzo
Just for my understanding.
Is there a way a transformer can perform faultless when no secondaries are connected and it starts smoking and smelling (like a cold charcoal grill) when there's current draw from a circuit?

[Gtr_tech]

Anytime you hear sizzling from inside the xfmr, its faulty. The sizzle sound is internal arcing....

[Daver]

Secondary load removed and it still sizzles and pops. New PT time! Thanks.
Dave

[doctorvoltz]

Make sure you fix whatever cooked it or you're gonna have another one on the grill

[g1]

It was replaced sometime in its life with an old Thordarson. The owner got it from some estate sale and said it was working briefly until it started smoking.

May be best to avoid brands containing the word "arson" in this unit.

[Daver]

The amp will be recapped and get a complete physical. Someone also added a choke to this thing at some point. That's coming out and the amp will be put back to stock. It's getting a potted Ampeg PT repro. Thanks!
Dave

[Prairie Dawg]

May be best to avoid brands containing the word "arson" in this unit.

Thordarson, Stancor, and Merit were the three main sources of replacement iron for the radio and television trades. Triad was there too but mostly on the west coast. Thordarson-Meissner was a good outfit that made a high quality product that was intended to be installed in the back of a color television and sit there in the cat hair and work without pause for 20 or 30 years. My guess is that this was probably installed by a radio and TV shop somewhere in this amp's distant past.