Output transformers and power tubes

[fredcapo]

I just received output transformer from Marshall for a JCM900/100w with same blown.

Installed now but not ready to power up since I don't have a tube tester to test th EL34's. The JCM has a shorted primary with a drifting ohmmeter reading. Am I too paranoid or is it likely that a bad tube contributed to the transformer failure? I am happy when an explanation of a failure is understood...

[g1]

Does that amp have the cathode fuses (op valve failure)? If so were they blown or incorrect value? I would also be very suspicious of the tubes that were in there when the OT primary fried.

[Enzo]

Help us out, JCM900 is a series of amps, not a model. What amp do you have?

[Gregg]

Considering the wire sizes used this OT will need serious "efforts" to blow. Check your mains and other fuses ratings.

[fredcapo]

Help us out, JCM900 is a series of amps, not a model. What amp do you have?

Funny thats the same question the Marshall Rp aked... It's the 100 watt 4100. Thanks.

[fredcapo]

Considering the wire sizes used this OT will need serious "efforts" to blow. Check your mains and other fuses ratings.

The transformer is definitely toast. I thought the rap was OEM OT's were not so robust.

[olddawg]

Maybe it's just me, but I would replace the power tubes if the OT was blown in any amp. And would be damn careful when I start to back up.

[fredcapo]

Problem is I did not include a quad of el34 when giving the repair quote. I may have to go with testing and matching if needed.