5E3 noise issues

[Jonny toetags]

Noticed a few problems with my 5E3 build now that i got it to the rehearsal spot and was wondering how to diagnose.

Here are the symptoms:
-There is loud feedback/oscillation with volumes cranked. The feedback seems to only start with the normal channel volume at 10 and until 12. It stops exactly at 10 when turning
the volume down. This happens with and without a guitar plugged in.
-The bright channel has a crackle/noise when playing notes. It is extremely audible. When I plug into the normal channel, there is no such noise.
-I also notice that touching the chassis makes noise.

A while back, i had a dead normal channel....i couldn't find the issue so i just unscrewed the jacks and put them back and it worked. Now I notice these issues.

I was just wondering could this all be related to a ground issue?
This is my second 5E3 build but the first one without a brass plate.

[Chuck H]

What you have is a parasitic oscillation. The amp is HF unstable at high output. This could be a lead dress problem or a grounding problem. It's most easily tracked down on a properly equipped bench with a signal generator, dummy load and a scope. Even then it can be tricky. If this is a straight forward 5E3 then make sure preamp power filters are grounded. Make sure there are no excessively long signal leads and try to route them away from the output. You might even try reversing the plate leads on the OT. Since the output is almost certainly involved this would change any induced positive feedback loop to a negative feedback loop and possibly stop the oscillation.

[Mick Bailey]

Did the amp work correctly up to the point where you had the problem with the dead 'normal' channel?

[Chuck H]

The bright channel has a crackle/noise when playing notes. It is extremely audible. When I plug into the normal channel, there is no such noise.

This could be the oscillation or a cold solder joint.

I also notice that touching the chassis makes noise.

It shouldn't. What sort of noise? Hum?