Crackling, worse with higher input, certain notes

[Boxnix]

My 5e3 that I love too much to blow up is having yet another mystery problem. I have seen lots of threads on this issue but none of them have ever posted the solution.

The crackle happens with higher input, when I hit the single coils hard or humbuckers do it with low volumes. When I play an A (any octave) it seems to be much worse although there is faint crackle with other notes if I hit them hard enough.

The amp did this a few months ago, I took it apart and poked at it, replaced the power tubes, the problem went away. I went on vacation and when I came back the problem was back. As far as I can tell the amp was not left on or dropped while I was out so I'm assuming the power tubes are still good for now, although I don't have any way to confirm that.

[Jazz P Bass]

What volume level.
Where is the Bass Control set at?
Did you try another speaker?

[Boxnix]

As volume goes up it gets slightly more crackly, but its bad at even low volumes. At some point the overdrive blends in with the crackle but it's still there. Tone does not have much effect on it. I have not tried a speaker. I'm going to take it out and look at it but I'm having trouble believing a speaker blown this bad would be an intermittent problem.

[Jazz P Bass]

Do you have any replacement tubes?
Probably as good a place to start as any.

[Chuck H]

I've heard what you describe on amps I owned long ago. I guess I've never tried to isolate it but I would guess that it's a mild parasitic oscillation. Crosstalk between different circuits in the amp. When there is more current running through the amp (like bass notes and hard chords) there is a greater EMF on certain leads being picked up by other leads. Good lead dress is especially important in these amps. Reducing bass in the preamp can often help. Not so much that you hear it, but maybe reduce the preamp coupling caps to .022uf instead of .1uf. The amp is actually recreating the lowest of low frequencies in the circuit itself but since the speakers can't recreate it anyway it's of no benefit to you and may actually be causing undue current on hard notes making the tubes clip or EMF crosstalk even though you can't hear the frequency responsible.

[Boxnix]

That makes a lot of sense. The wire in this amp is a total mess, all melted and tangled. I am thinking about ordering new caps and resistors and just redoing it. I always wanted an amp project. I bought it off some guy who bought it off another guy, no idea who made it.

[frankeg]

I've seen/heard a bad/cold solder joint do this. It was a poorly soldered coupling cap. I found it by chop sticking the amp (I actually use an old wooden spoon) with the power on and nothing connected to the input jack. Just tapping the cap (orange drop) brought on a loss of volume and crackle. When I pushed harder on the cap, it cleared up. Prior to finding that, I had days where it played fine but then the next day it didn't. I felt very lucky to have found it.

[frankeg]

"The wire in this amp is a total mess, all melted and tangled."

I missed that...Sorry, poor attention to detail... I'd definitely start with the wiring but at some point you have to ask if it's worth it... Some aren't! I bought an old PA off ebay once to use the iron for a build. The PA worked but had a howl at about 1/2 volume. I wasn't concerned since I was re-building with new chassis and components... Well I built a really nice PP EL 84 out of it that had a howl at about 1/2 volume... Go figure...It sits on a shelf now. I'm about 80% convinced it's in the iron. Some day I'll find out for sure...

[Boxnix]

New info, the problem goes away after it warms up for a while. Do tubes behave this way? I'm leaning more toward the bad connections and wire dressing. I think I'm gonna gut the chassis and start over. It looks terrible, lots of things melted in there and I'm starting to think it's burning the tubes up, might not be biassed very well. Going to pick up a backup amp tonight. Project time!

[thumbs]

Although the problem could be a lot of things, you might try testing the input jacks before moving on. If the problem goes away when plugged into one of the jacks but not the others, replace that one. I've had to replace two on my 5E3 clone. From what I hear, it's pretty common.

[cagamp1]

That makes a lot of sense. The wire in this amp is a total mess, all melted and tangled. I am thinking about ordering new caps and resistors and just redoing it. I always wanted an amp project. I bought it off some guy who bought it off another guy, no idea who made it.

If you are literally serious about the melted wire, I'd say that is probably your source. Change out the wire and check for any bad or damaged components connected to them.

[loudthud]

New info, the problem goes away after it warms up for a while. Do tubes behave this way? I'm leaning more toward the bad connections and wire dressing.

It could be any just about any connection in the amp, a bad tube, tube socket or a bad speaker. You need to try the amp with another speaker, locate the speaker on the other side of the room to isolate the amp from any vibrations. If that eliminates the crackle, try the exsisting speaker but remove the amp from the cabinet and use some kind of extention cable. Once you have eliminated the speaker but know that vibration sets off the crackle, the chopstick test is the best way to locate the bad connection or bad component. Wiggle each terminal on each tube socket and do the same to each component and solder joint. Sometimes a solid wire will break inside the insulation so wiggle each wire.