5E3 blown OT?

[cminor9]

Ok, I messed up. I fired up the 5E3 tonight, and after about a minute discovered that my speaker wasn't plugged in. When I grabbed my guitar cable from the back of the cabinet, I knocked the speaker wire loose (it was disconnected from the speaker.)

First, I think I'll solder the speaker wire to the speaker instead of rely on the spade terminal. Lesson learned.

Second, can someone please help me? The amp works now, but it has a HORRIBLE hum (a loud buzz). I can still hear my guitar, and it sounds as good as always. It just comes with a loud buzz now.

With nothing plugged into the input, it's normal. With a guitar plugged, I get a bad hum which gets worse the hotter the signal, like if I plug in a guitar with humbuckers and/or turn up the volume on the guitar. I changed the tubes, and that did nothing. I moved it to a different room to eliminate interference. Would a shorted OT cause this loud hum? Any ideas? Are there any other parts I should check beside the OT and the output tubes?

[richon]

i don't think it is the OT, maybe you should check other problems inside your amp.

if the amp only buzzes when a guitar is plugged i think it is the schematics or a preamp tube.

[Enzo]

If it only makes this noise when teh guitar is plugged in, then I'd start suspecting the guitar or the guitar cord.

[cminor9]

Ok, thanks guys.

One more thing: I played the amp two days ago with the exact same setup (guitars, cables, etc) and it sounded just fine, the amp didn't hum or buzz before.

I'll try some more part-swapping and come back.

Thanks again.

[cminor9]

Well, I plugged the amp into a different part of the house with a different guitar cable. It worked and the hum was much better, though it still seems to hum more than before. The other day I put it in the back of my SUV, drove across town, and played at a friend's house. Maybe I knocked something loose driving on these rough St Louis streets and that's why it's humming. I'll have to investigate further.

I did notice some burnt debris rattling around in one of the power tubes, though. I think the poor power tubes took the brunt of the infinite load. Better them than the OT, though the tubes cost just a little less than a replacement OT. But it seems the OT is ok.

You guys who repair amps (like Enzo ), what do you typically see go wrong first in such a scenario, when an amp is turned on without a load? Also, wouldn't a shorting jack for the speaker jacks prevent damage to the amp?

[Tremolux55]

A quick thing check the input jacks. I had my tweed Champ copy suddenly go noisy when I dropped it (from a low height - oops!).

Naturally you assume the worst, after changing out the pre-amp and power amp valves no difference. Then I tried the chopstick test on components as the amp was running and it turned it was one of the shorting jacks playing up.

Hopefully it'll be spmething simple like that. Good luck with it.

[cminor9]

Yep, it was nothing. I poked around in the amp with a chopstick for a while the other day and I found a loose connection and fixed it. Maybe that was it, since I played it for about four hours last Saturday and it was super quiet. Funny how that works.