I have an '87 Marshall SJ 2550 that is emitting static noises.
- I cannot hear it when the amp is turned up.
- The static noises do not increase with the volume, nor is it affected by the tone controls.
- It IS affected by the presence control! Gets brighter as I increase the P control.
- It stops when I switch the amp into SB mode, and begins as soon as I remove it from SB.
- If I let the amp cool and then turn the amp on, it doesn't do it right away. I have to leave it on for about 15-20 min for the static noises to resume.
Here's what I've done so far...
1. It's not in the preamp. The volume and tone controls have no affect on the noise. I did change the tubes, just in case... No affect.
2. It's not the power tubes. I'm using a proven pair of =C= EL34's that have less than 30 hours on them. Was doing the same thing with the previous set of tubes as well.
3. I've done the "poke around with a chopstick" thing, but found nothing.
Any ideas on what could cause this?