Mesa Boogie Recto 3ch - NO clean channel

[godmustuseaboogieman]

That's not what I want to hear!

The voltages are all between 454-457. As previously stated point B is ~455 (a little higher today), I guess that means those resistors are fine.

What's the best way to check the OPT?

EDIT: Some more info...

When I run a sine into the FX return with a meter over power point A, the HT drops from 450ish to 407ish. This is with Silicon rectifiers and 'Bold' setting.

I've heard of HT sagging, is this much expected or could this be part of the issue?

[g1]

Sorry I had to mention the OT, here are my reasons: you tried other output tubes, no change. You checked output tube plate, screen and grid voltages and all appear good. You had clean(ish) signal at the phase splitter plates but weak distorted signal at the output. You have had problems with blown fuse and red-plating. Maybe a bit more info about the level of signal you had at the phase splitter when you got 1volt output would help, you were looking with the scope?
This seems to have exhausted most of the usual suspects leaving the OT. Hopefully I have missed something someone else here will pick up on.
As far as the sag in the high voltage, it is more likely a symptom of the problem rather than the cause.
For the OT, first check the resistance from the center tap to each of the plate connections (power off and caps discharged). This test is more likely to show if there is a gross fault in the primary, which is not likely the problem.
Beyond that, the easiest test is to swap in a known good OT, doesn't need to be exact type, just something for a push pull amp of 50watts or so.
Also there is this simple tester: http://www.geofex.com/FX_images/xform_test.gif

[godmustuseaboogieman]

Not nice!

But thank you for all your help.

I don't have another OPT lying around, There's a few JTM45 ones from a UK distributor here Vintage / Classic Guitar Amp Transformers.

They don't seem to cost stupid money, would one of these do to check? I dont mind throwing £47 at it to test, but £100 is a different story!

I'll try the other checks you suggested first.

[godmustuseaboogieman]

Hi All,

I tried a transformer from that site in place of the mesa TX. It squealed like a banshee... I guess something to do with a difference in the DC resistance of the primary? Dunno. But it wasn't any louder.

Has anyone got any more advice for me please?

[52 Bill]

It squealed like a banshee... I guess something to do with a difference in the DC resistance of the primary? Dunno. But it wasn't any louder.

How could you tell? The squeal is caused by positive feedback, reverse the two primary winding to plate connections and see what happens.

[godmustuseaboogieman]

Hi Bill,

there was guitar signal coming through... and it was still distorted and quiet.

[godmustuseaboogieman]

Dear All,

Thank you for your help. It was only as I woke up on Sunday morning that I thought that the fault could be a short across the slave Out. One of those Eureka moments. Replaced a faulty pot and the amp seems to be fine now.

Cheers,