ARG ! Amp buzzing more than it normally does

[iknowjohnny]

I decided to lift the turret board and check all solder connections underneath, then replace it and continue cleaning up all the sloppy solder joints and all from years of tweaking and changing things. Well, i've done this before a couple times so maybe close to a year of it. Big mistake. Now the amp is buzzing a lot when before it was a very quiet amp. I was hoping maybe you all might have some suggestions for troublshooting it i haven't thought of. I don't have a scope, so that won't be an option. Here is what i have done so far

1)-chop sticked every wire and solder connection from here till tuesday making sure that is not the issue. I also made sure it wasn't a wire under the board.

2)-checked every ground connection in the amp.

3)-checked the pots and clean them all with deoxit, and cleaned all jacks

4)-checked for DC leaking thru caps

5)-replaced a few suspect caps

6)-swapped out every tube

Any suggestions you have would be greatly appreciated, as I am pretty much out of ideas.

[Firestorm]

Can you tell if it's 120Hz post-rectifer noise, or 60Hz AC or ground loop noise? Try to isolate the stage it's in: remove PI tube to see if power amp hums by itself. Check specific preamp stages by pulling tubes or shorting across the plate resistor.

[Gibsonman63]

divide and conquer. Just a couple of thoughts:

Have you tried pulling tubes? Pulling the PI will tell you whether the problem is in the preamp section or the power amp section. You can replace pre-amp tubes and work your way to toward the first stage.

Is it possible that cleaning up the soldering has created a better path to ground and caused a ground loop becuase there is now more than one path to ground?

I used to sometimes forget to turn off my florescent workbench light when I was done soldering and ready to test. Drove me nuts for a while.

(a little redundancy here. Firestorm posted while I was still thinking!)

[iknowjohnny]

Thats another thing i forgot to mention....i did turn off everything in the room even tho nothing has changed in that regard since it started this. As to PA or pre, i will try pulling tubes and get back to you. Thanks for that.

[iknowjohnny]

Ok, pulled one AX7 at a time starting with the PI and the amp is dead quiet with any of them pulled. I guess it's somewhere between the input to V1B. So i'll start looking closer there. Thanks

[Structo]

That's strange that it isn't a tube causing it.

Have you done anything different with the amp?
Have it sitting somewhere different?

Something different plugged in.

Is the input jack working by shorting to ground when disconnected?

I take it this is one of your new builds?

[iknowjohnny]

No, same old amp i'm always playing around with. And nothing is different since it was quiet other than i just cleaned up all the solder joints that were sloppy. Everything including where it sits, the room etc are the same. Just quiet as a mouse, cleaned it up, now buzzing. Nothing in between. Input does short when plug removed, tho i will tell you i checked that and it WAS defective. I just shot some deoxit on the shorting tab and not it shorts perfectly now, but the noise remains.

[iknowjohnny]

Well, i tried whole different input by soldering a jack and 1M resistor to the grid resistor, checked the preamp supply, replaced the coupling caps and plate resistors on V1, hit all the solder joints there. No change. This is really a drag. Tried it with all my guitars and another cord by the way so thats not it.

[Cliff Schecht]

Did you triple check all of your grounds to make sure they have a solid/tight connection?

I recently helped someone troubleshoot a noisy amp build where the issue was they forgot the 100 Ohm faux centertap resistors. Where is your center tap going (real or fake)?

Pictures might help..

[iknowjohnny]

Yeah the grounds were the first thing i checked. There are no center taps resistors and the PSU grounds are bolted to the chassis with a bolt then another to lock it.

[Firestorm]

That's strange that it isn't a tube causing it.

Well, we don't quite know that. Pulling V1 removes any effect of the tube and the input. Since the input has now been redone, I think that leaves V1 as the suspect.

iknowjohnny: What does the V1 circuit look like? Using both triodes? 60Hz or 120Hz?

[iknowjohnny]

I don't have a scope. I also swapped all the tubes and V1 has has several different ones. Sockets are belton and tight, tho maybe i'll have a go at cleaning them and checking all pins for tightness.

[Firestorm]

You may have to think through whether the grounds are in the right places. Sometimes a very small resistance will keep stray currents from showing up in places where they shouldn't be. When you cleaned up your solder joints, you may have removed a resistance that prevented the problem. Based on what you found in pulling tubes, I still think the area to concentrate on is V1.

[iknowjohnny]

yeah, i suppose. I just don't think theres anything left there. I swapped every resistor and cap so far. I just checked the socket tension and deox'd it, tho it obviously wasn't necassary. Those beltons are fantastic !

[Gibsonman63]

Have you checked the wire from the input jact to V1? When I did my build, I noticed that the insulation on the shielded cable melts really easily.

You might try measuring resistance from the ground side of each component that gets grounded to your chassis.

Try a humbucker equipped guitar or a different guitar just for grins.