5E3 build - noise

[lowell]

This amp was actually built quite well. The owner built it and complains of noise. There are 2 noises. 1 is 120hz and 1 is a static, crackle and pop sort of issue. I grounded pin 7 of V1 with an alligator clip and the noise stops. This led me to believe the noise was from a bad input jack (shorting type). I checked 'em all and they're functioning properly and wired correctly. I the suspected the 68k grid stopper solder joints and the 1meg grid leak, so I retouched ALL solder joints related to V1. Still no fix. I then poked around on the fiber board and if I push on any component or the board towards the area near V1 there is more static, crackes, pops etc... I then replaced both 68k grid stoppers going to V1B, both plate resistors for V1, and the cathode resistor as well. Still problems. Oh and I shouldn't forget that I DID try a brand new JJ ECC83 and still problems. I'm beginning to suspect that this board is microphonic and/or conductive. If I even lightly touch any component with my chopstick it effects the noise, and lessens the noise. If I grab the coupling cap from V1 to V2 and wiggle it with my hand there is more crackles and pops. Short of replacing the board, wires, and/or components I don't know what to tell the owner.

[booj]

Re-flow all the solder contacts in the area that the noise is coming from. I can't tell you how many perfectly clean shiney solder connections I've found that were intermittent and the cause of noise like you have described.

[frankeg]

If it's not solder joints as mentioned above then:
If I understand you correctly, you have a Fender style fiber board? If so, there is a possibility that some loose or excess solder between the boards is the culprit. If the boards are not too tight, you can try to increase the "air" gap by sliding a small piece of non-conductive material between the boards around the area in question. Another known issue with fiber boards and you know is moisture. You can use (carefully) a heat gun or hair dryer on it to see if it improves.

[lowell]

How does adding an air gap help? Curious. I've tried almost everything. I replace most related components, resoldered the entire under-side of the board... still noise. It did seem to me that the noise lessened after soldering the board. I am gonna try replacing all related wires as these wires seem oxidized and are hard to tin. I hope that does it otherwise I feel the only other option is rebuilding with new wires and a new board.

[frankeg]

How does adding an air gap help? In your case, it doesn't since you've gained access to the underside of the board and re-soldered everything. As you know, the Fender double fiber board is usually very tight and you have to un-solder a lot of wires just to get a peek at the bottom of the eyelet board. "If" there is an issue with a conduction path between the boards due to solder debris or moisture, you can sometimes "fix" it by inserting a piece of shrink tubing or a popcicle stick in the area of question. It's more for separation than increasing the air gap - poor analogy in my 1st post... I have several old Fenders with multiple pieces of shrink tubing poking out between the boards. I live in Pennsylvania where humidity is huge in the summer.

[lowell]

Okay so I replaced most underboard wires that went directly to the 1st stage. I then replaced the grid wire from the 68k grid stoppers to the grid of the tube with belden shielded 2-conductor wire - THAT seemed to do the trick. I think that running unshielded grid wires between these boards creates some sort of capacitance effect causing problems. My theory anyway. In any case it seems to have fixed this ever so annoying and tough-to-troubleshoot problem.

[frankeg]

Good to see you fixed it! I will keep your solution in my notes. BTW, in my previous post I mistakenly said that I have several old Fenders (I wish). I meant to say I have seen several like that. The Hoffman amp site has some technical notes on the Fender board issue as well if you're interested.