Right channel noisy. Help troubleshooting

[denti alligator]

I don’t see any.

I haven’t tested the voltage with speakers attached. I can try that tomorrow. But I’m assuming I would have seen the wandering when I did the voltage test earlier, and I didn’t.

I did notice, though, that the voltages were slightly lower on the right channel. I think. I can double check tomorrow. Nothing dramatically different, but still.

 

[2wo]

Just a thought, run the hum pot on that side back and forth a number of times and reset for lowest noise, can't hurt....John

 

[denti alligator]

I tried turning the hum pot when I first was troubleshooting. Made no difference. I can try again.

Paul, when I test the voltages again later today do you want me to leave the jumper in or remove it first.

 

[Paul Birkeland]

You can leave the jumper there.

 

[denti alligator]

OK, no obvious fluctuation in voltages when the noise comes in. No green visible anywhere.

Here are the voltages:

1:382
2: 399

6: 53.8
7:216.2

21: 54
22: 54.6
24: 54.7
25: 54.1

For comparison (the left channel, which works fine):

14: 210
15:56.5
19: 398
20: 370

36: 56.8
37: 57.4
39: 57.4
40: 56.7

 

[Paul Birkeland]

At this point I would suggest running the amp for a week straight without turning it off, then revisiting the issue.  If there is some partially conductive goo still in there somewhere, it may burn out over time or make itself more obvious if the amp is allowed to run for a considerable time period.

 

[denti alligator]

At this point I would suggest running the amp for a week straight without turning it off, then revisiting the issue.  If there is some partially conductive goo still in there somewhere, it may burn out over time or make itself more obvious if the amp is allowed to run for a considerable time period.

Will do. I’ll report back next week. Or sooner, if it somehow disappears before then.

(It’s quiet now … was noisy a few minutes ago… )

 

[denti alligator]

Quick update: nothing definitive yet, but it’s been on for 16+ hours now and although I can’t right now sit next to the speaker (or even in the same room), I was just downstairs and sat there for about 5 minutes (it’s rarely silent for more than a minute) and it was completely silent.

I remember when I first got it back from you, Paul, I turned it on and immediately put music on, so I didn’t hear the noise right away (I was listening to LPs, so easy to take the noise for static on the record). That night I accidentally left it on and in the morning I did not notice any sound. It wasn’t until I turned it off and then later back on that I heard the noise.

Also, you said you ran it for 40 hours straight with no noise. So maybe it goes away as the amp gets really warm?

Does this helps identify the possible source?

 

[Paul Birkeland]

This would be consistent with the contaminant hypothesis.  If the contaminant makes semi conductive pathways in the amp but these burn off as the amp runs, you may be able to just cook this off by leaving the amp running continuously for a week. 

 

[denti alligator]

Fingers crossed

 

[denti alligator]

I've been sitting here now for about 15 minutes or so, maybe slightly more. And it's been totally silent, until a second ago, when there was one brief burst of noise. Now it's quiet again. So I doubt it has been totally quite the whole time.

 

[denti alligator]

Woke up this morning and it’s noisier than ever. 

(Edit: it’s pretty chilly in the morning. Heat kicked in and since then it’s been silent…)

 

[denti alligator]

Little over half way through the week. It’s been running non-stop. Sadly the hope I had around days 2-3 has vanished. It’s been pretty consistently noisy for the last couple days. It does sometimes go for longer without any noise at all, but rarely for more than a minute or two. 3 days to go. Maybe it will burn through whatever contaminant is in there after all. I’m not counting on it, though.

 

[denti alligator]

OK, so it’s been a week that the amp has been on. This morning it is still making that same noise. Where do we go from here? I am willing to begin replacing parts on the right channel, if that’s what it takes. But it would be good to know where to begin. I’d rather move slowly and replace one part at a time to see if it makes a difference. I have wire. I would need new resistors and capacitors, if these might be the culprits. I could order these myself or if possible I would happily buy them from you.

 

[Paul Birkeland]

Since grounding the grid of the 2A3 allowed the noise to remain, you would want to replace:

4 pin tube socket (if it isn't the one I already replaced)
Both terminal strips bolted to the 4 pin socket
The 2K and 3K resistors
The 220uF bypass cap
The hum pot
The 22 ohm resistors

That would be my next step based on the information provided; it is not necessarily the solution.

 

[denti alligator]

Thanks. What about the

220ohm carbon film resistor (red, red, brown, gold)

and

0.15ohm 3W (brown, green,
silver, gold, violet)

 

[Paul Birkeland]

Those are parts are unlikely to create noise problems if there's semi-conductive residue on them.  The grid stoppers because there's no current flowing through them, and the 0.15 ohm resistors because they are already such low resistance that they are unlikely to be influenced by anything short of a dead short.

 

[denti alligator]

OK, thanks. I'm getting the parts from Eileen. The socket is new (the one you put in) and I have extra 2K wirewound resistors. I'll start by replacing the 2k resistor, which I have on hand.

 

[Paul Birkeland]

I would suggest doing it all at once if at all possible.

 

[denti alligator]

I would suggest doing it all at once if at all possible.

OK, will do. Though it would be kind of nice to know what, exactly, was at fault—if indeed any of these replacements fixes it.