Ampeg Reverberocket: intermittent noise problem?

[_Paulito_]

My friend's Ampeg Reverberocket 2x12 (reissue; I think it's late 90's/early 00's) generates a scratchy intermittent noise (kinda like loud static) when I play low freqs (low E open or first few frets), doesn't occur at higher frequencies.

I had the exact same problem with a (solid state) Line 6 Flextone II; turned out to be bad poweramp chip (LM3886TF); replaced and problem went away.

This Ampeg is a tube amp; however, I don't know if there are any SS components that might cause a similar problem, or if there are other possible root causes (cracking solder joints, bad caps, bad transformer connections, etc).

Can anyone offer advice? What other info can I provide to help diagnose?

Thanks in advance
- Paulito

[Chevy]

Well, just off the cuff, since you're not saying the noise also appears when you wang real hard on, say, a 3rd position loud G bar chord or something like that, that the problem may be frequency-vibration related.

(At this point I don't really know if it's an part failure or an electrical connection failure. )

What happens when you tap/rap the cabinet? Each of the tubes? If it comes from the tubes, well, that's a pretty good clue right there. But if rapping on the cabinet does make the noise, take the amp out of the cab and start poking leads with a chopstick or something, tapping other components, jacks, etc as well to narrow it down.

If it's an electrical part (ie a filter cap) failing, you'd think that the noise might be duplicated by pushing the amp louder on slightly higher frequencies. But perhaps not. If it's bychance a failing electrolytic in the signal path, I'd think you'd pretty much have to put in a 70HZ tone in the front end, and see where it fails in the signal path.

Hope this is of some help.

[_Paulito_]

Chevy - thanks for the feedback; it was helpful. An update:

- replaced the power tubes; noise went away

Couple other problems I mentioned in some other thread:

- low hum, not affected by any knobs; went away if the amp is tilted just slightly. Also went away when power tubes replaced; I read in a thread somewhere that the hum is associated with bad power tubes

- Volume was intermittently cutting out (for a few minutes) and coming back, and repeating. I went sniffing around in the two PCBs and found a few bad solder joints and loose wires. Resoldered, tightened wires, problem went away.
Not sure if root cause was also power tubes though.

Amp tests fine after about 0.5 hr playing, I think it's OK now