Blues Jr reverb hum

[Randall]

Green board BJr. Reverb hums. Checked connections, re-terminated cables at board as one shield was iffy. No change. Hum apparently coming from output of tank, and changes as I move that end of the tank farther from the speaker. Goes down appreciably if I push the tank to the front of the cab bottom. It has a MOD 8EB2C1B tank. It came in with a loose 1/4" input jack connection issue, and I only noticed this hum after I put it back together.

Is this a thing with these? Should I just push the tank away from the speaker? I don't want to re-engineer it since it didn't come in with this complaint.

[Enzo]

Chances are it is not the speaker, but the power transformer. We are talking 60Hz hum, right? Easy to verify, pull wire off speaker and connect amp to external speaker. Now does reverb still hum, and does moving it matter?

In any amp, make sure OUTPUT end of reverb pan is farthest from the power transformer. Some amp makers add a metal plate as a shield over the open side of the pan, often just the OUTPUT end half. And some pans are in bags upside down. That leaves the open side exposed to the transformer field.

Worth checking.

[Randall]

Hooking up a different speaker makes no difference in the hum, and I don't see why it would, the original magnet is still there. I was probably just parroting something I read about it in some google search. Actually, it seems to be the power tubes that are the source of the noise. I just relocated the tank to the back corner of the floor with the jacks facing away. That puts the output jack in the corner. This seems to be the best and easiest solution.

[Helmholtz]

Hooking up a different speaker makes no difference in the hum, and I don't see why it would, the original magnet is still there.
Actually, it seems to be the power tubes that are the source of the noise.

Neither a speaker magnet nor the power tubes generate a magnetic hum field, but the PT does.
Magnetic fields are directional, so not only the distance to the PT but also the orientation of the rev. recovery coil matters.

[nosaj]

Actually, it seems to be the power tubes that are the source of the noise. I just relocated the tank to the back corner of the floor with the jacks facing away. That puts the output jack in the corner. This seems to be the best and easiest solution.

Is the current balanced between the 2 tubes?
nosaj

[Randall]

All I know for a fact is the noise got greater when putting the output jack of the tank closer to the EL84s, and to a little lesser degree, the preamp tubes. I do not dispute the PT can cause hum, but it does not seem to be the source of it in this case, whatever the physics are. The noise had more in common with a bad preamp ground than it did PT hum. Could be something with the MOD tank I suppose, but it's gone now.

I did not check the current match of the output tubes. It wasn't in for that.