Right channel noisy. Help troubleshooting

[denti alligator]

If this is the case it kills me, because that means I actually had figured out the problem (I even contemplated buying a new socket), but screwed up my testing. Talk about face palm!

Still, I simply cannot understand how I could have mixed up the wires...

Oh well, at least I'm also getting the right shunt regulator resistors installed. 

[denti alligator]

So, as I suspected, the source of this noise could not have only been that tube socket that Paul replaced. I received the amp back from him and there is still noise in the right channel. Only the right channel. Same as before.

Paul says the green residue is the source. However, I don’t see any of it on the right channel (now that the offending tube socket was replaced—however, remember that that socket was until the very last minute in the left socket and I never heard noise there). In fact, I see a tiny bit of this green residue on the left channel right now, but there is no noise in that channel. Never has been.

All I have ever used on this amp was 60/40 rosin core solder and deoxit. I’ve used solder wick (the copper ribbon kind), but that shouldn’t leave a residue. And I’ve used a Radio Shack solder tip cleaner. That’s it.

Suffice it to say I am very frustrated. I just spent over $300 for a repair, and while Paul fixed some things for me, the problem for which I sent it in has not gone away. Paul can chime in here. But I don’t understand his explanation, which does not account for how the noise is isolated to the right channel only.

At this point I’m going to have to live with it. Most of the music I listen to will drown it out. But I needed to vent a little and was hoping someone else might have some ideas or insights.

[Paul Birkeland]

We are just going to refund you since I was unable to successfully repair your kit.

-PB

[denti alligator]

I am going to try and clean the offending area. Paul, could you please tell me what that area is. You said you had a narrowed it down to a specific area (power output). Knowing exactly which terminals to focus on would help.

First I’ll clean these. Suggestions: deoxit? Rubbing alcohol? Toothbrush? Cotton swabs?

If that doesn’t work I will remove solder and resolder.

If that doesn’t work I’ll try the dishwasher method.

Again, I cannot determine the source of this green contaminant. I’ve only ever used rosin core solder, deoxit to clean, desoldering wick, brass solder tip ‘scrubber’, and solder tip cleaning paste.

The cleaning paste contains tin and ammonium phosphate. Could these be at fault?

The desoldering wick is of course copper, so maybe it is to blame?

Google led me to some discussions of flux causing issues. I have rarely (if ever) cleaned off flux while soldering. Should I be? I will play around with my basic materials and an unneeded white ceramic socket I have and see if I can replicate the green contaminant.

[denti alligator]

We are just going to refund you since I was unable to successfully repair your kit.

-PB

You don’t need to do that, especially if I can count on further guidance from you on this matter (see previous post). I do really want to get to the bottom of this.

[Paul Birkeland]

In our lengthy e-mail exchange, I posited a likely next step.  Do I also need to post that here?

[Doc B.]

Paul contacted me about this and I agreed with him that it is appropriate to give you a refund since you still have the noise issue. We were away from the business this weekend but you should see it today. And we will continue to support you here to try to resolve the issue.

It is frustrating when we send something in for a repair and the thing we wanted to get fixed is not fixed. I could tell you stories of my own from both sides. After experiencing this a few times over the years it seems to me that sometimes the issue is elusive enough that it doesn't manifest itself very often. That can make it difficult for the tech to verify resolution absolutely in the time they can allot to the project. What Paul did find - conductive tracks of corrosion across the one tube socket - is certainly something I would have assumed to be a red flag and his replacing that socket was the appropriate course of action whether it was the source of the noise or not. It is unfortunate that it did not resolve the noise but it was imperative to fix from the standpoint of functionality.

Not sure if ammonium phosphate could cause the corrosion issue but I had experiences in the past with corrosion appearing after a while on terminals when I used a sal ammoniac block - ammonium chloride - for tip cleaning. The dishwasher cleaning method can be a pretty effective means of removing stuff that you don't want to be on the connections whether it be flux or other contaminants. Just make sure the components are completely dry before testing and powering up.

[denti alligator]

OK, I guess I will try the dish washer method. Is a heat dry cycle safe or should I just take it out an air dry when it’s done?

I inspected the amp again yesterday and could not find any traces of the green residue, except on the other tube socket. But I’m not getting any noise on that channel! Is it possible that something is allowing for the interference from this green stuff to move channels? That would explain, in part, how replacing the right socket (that was on the left for most of the troubleshooting) mitigated the noise but didn’t eliminate it.

Also, I tried playing around with an unused socket: soldering, desoldering with wick, using the tip cleaner, etc. No green residue. I don’t know where it came from.

I looked at the old Sovtek 2A3s, since one of these failed on me a few years ago, and there’s no trace of anything on them. But the Shuguang tubes I have in there now look different. One of them has a tiny speck of green on it and it looks like there may be (very hard to tell without magnification) green underneath the pins (where the pins meet the ceramic base). Could this stuff be “leaking” from the tube? (Note that switching tubes from channel to channel makes no difference.)

[Doc B.]

My logic flow for this

1) we don't know the exact cause of the noise problem

2) we've seen corrosion on the amp somewhere and we know that corrosion can cause similar problems

3) there might be corrosion somewhere in the noisy channel that is hidden - maybe under solder joints, maybe up inside the gap between the tube pin terminals and the ceramic, maybe elsewhere.

4) dishwashing might solve the problem based upon our past experience, and it is less intrusive than replacing parts until the noise subsides

I don't feel I can offer any other useful speculation until that has been attempted. The best bet is probably to try the dishwasher method, make sure the amp is absolutely bone dry, check all the resistance readings and then check all the voltages. Then run the amp and see if it has resolved the issue. At that point we can regroup and see where we are at.

[denti alligator]

Great, thanks. A couple more questions before I proceed:

1. Is the heat dry cycle of the dishwasher going to be safe (it gets awfully hot).

2. I'm assuming I take out the tubes and don't include them in the wash.

3. There is some weird black gunk on parts of the amp that wasn't there before. Looks like it could melt (further). Should I try and remove this? Paul, can identify this?

[Doc B.]

if your dishwasher's dry cycle gets hot enough to melt plastic kitchenware then it's probably not a good idea.

Yes please remove the tubes

The black material is a high temp adhesive that has been applied to the capacitors to keep them from getting knocked around in shipping. It can stay.

[denti alligator]

Non-dishwasher safe plastic can get warped/melted, especially if put on the bottom. I could put it on the top and minimize the dry cycle? I just want to be sure I don’t inflict more damage.

[Doc B.]

Can't really speak to this with any certainty but that probably makes sense. Might be a good idea to let the amp sit for some time afterwards too, to be sure all the nooks and crannies get dry. It couldn't hurt to blow a fan on the chassis for a while.

[denti alligator]

Thanks, Dan. I looked into it and apparently my dishwasher reaches 150 degrees (Fahrenheit). So long as that’s not too hot, I will run it. Paul mentioned the possibility of discoloration. Is this from the heat or the water? What if I put a cover on the top and leave the bottom open to get the majority of the direct water spray?

I’ll probably try it tonight and then let it dry overnight.

[Doc B.]

Electronic components are typically rated for 85C which is 185F. Darkening of the raw aluminum panel can occur if you use detergent containing phosphates. If the top is covered I would guess that water will get trapped inside. But I have not covered the top so I don't know what the result would be.

Instead of using the dishwasher's dry cycle you can put the chassis in an oven set to 170F after cleaning.