Dead amp

[straycat]

A friend brought me an amp today to look at it and see whats wrong with it.
He thinks its a bad tube.
All the tubes glow and seem to be fine.I asked him what impedance speaker cab he had and he wasn't sure my guess its a 16 ohm cab being a Marshall 1960.
Well he said his guitar player said you could use the 8 ohm input or the 16 ohm so he said he used the 8 ohm input.
My guess he popped a tranny am I correct in thinking this?

[Twitch]

Not necessarily. Need more info. Tubes glowing due to heaters but other parts of the circuit may be bad etc.. Does the amp make any noise at all? What happened when it stopped working? What make and model amp is it?

[straycat]

Its a Jet City Pico BTW
The tubes glow just fine not cherry red on the plates or anything obvious.Sockets all look good.
Tried some other tubes but still no sound.Fuse is fine I checked that first before turning it on.
He told me he was playing it and heard a pop then it went silent but the power was still on.
No smoke or burned smells.
I opened it up and no burned resistors or caps.Wires to all trannys look fine too.

[Twitch]

Well, nothing obvious comes to mind with that info either, sounds like a trouble shooting project now. Without seeing best I could offer is if it has an effects loop or preamp out, see if just the preamp produces signal from the send and/or the preamp out, and then if it has a return see if the power amp produces sound from a different source. If you have nothing from the preamp, then I would suspect a component somewhere bad or even the standby switch(though a bad switch is usually accompanied but that nasty burnt electronics smell). If there is preamp signal then I would suspect perhaps the OP tranny, though I cant think of a way to test it unless you just happened to have a replacement. In addition, transformers USUALLY dont go belly up for no reason, so maybe a bad tube as well or something else could be the root problem.

[jgcable]

Usually, a bad tranny would smell really bad. If you heard a pop its possible that an internal board mounted fuse may have tripped?

[straycat]

I guess its off to an amp tech because I can see nothing wrong visually.

[lerxstcat]

Those things just came out, didn't they? Like within the last 3 months? Should be a warranty situation that soon.

[straycat]

I think he bought it used or traded for it.

[Cygnus X1]

I've seen plenty of output transformers short out with no apparent signs of damage.
Power transformers "blow".
Output transformers usually either pop or fizz out.

Did you say you replaced all of the tubes?

[DonP]

Did you say you replaced all of the tubes?

Yes, he said that.

Stray, do you have a DDM and know how to use it? Just remember safety when you do. Ground one lead. hold the other, and your free hand goes in the pocket (to prevent you from becoming a circuit).

[straycat]

DonP I can change tubes but working on the internals I have never done.Fixed a fuse holder a few times but that was easy.

[DonP]

Ok, better go with a tech.