Any procedure to test around an output transformer?

[fredcapo]

RG Thanks. Yes. the tester seemingly works as advertised on good transformers. The bad OT's as mentioned have hard shorts mostly on primary side. I due to inexperience did not
jump to test the OT's early on.

[Steve A.]

The usual transformer shunt method of measuring bias current effectively shorts the plates to B+ so you could completely disconnect the OT primary and give it a quick test with the plates connected to B+. If that doesn’t blow the fuse the OT must be the problem.

Makes sense to me. Thanks!

Steve

[Steve A.]

Be sure to test your tester...

While we are at it we should jail our jailer and tail our tailor!

[Mick Bailey]

I assume the OT failures are primarily spontaneous and due to poor quality. Did the older "quality" amps have a proportional OT failure rate?

Pretty much all of the OT failures I see are fairly recent amps, including the OTs fitted to the Tweed '57 reissues (which are MM). I rarely see older amps with failures. They're spontaneous failures in the main, usually shorted turns or opens on one side of the primary, with no other fault present.

[Jazz P Bass]

You gotta love that podink OPT that Fender puts in the HR Deluxe amps.
Ca_ching goes the cash register.

[Enzo]

I have never had to change one.