Right channel noisy. Help troubleshooting

[Paul Birkeland]

Next you'd want to put a clip lead back across the 249K resistor from 2A3 grid to ground on the noisy channel to see if the noise is still present.  When you performed this experiment previously, the noise was unchanged, and it would help to know if that's still the case or if this eliminates the noise.

[denti alligator]

OK, I clipped a lead across that resistor as before and the noise is still there. Note, however, that it is significantly less constant and loud.

[Paul Birkeland]

Now swap the 2A3s to see if the nature of the noise changes.

Also if you have to press your ears up against your speakers to hear what you're hearing, that would suggest that the amp is quiet enough.

[denti alligator]

Yes, same noise with tubes swapped. I can hear the noise from 10 feet away. It is quieter, though, and less frequent. But then again, when I left it on for a week I had a day or two when it was similarly less constant and less loud. My comment about putting my ear up to the speaker was just to confirm that the low-level noise is indeed constant, unlike in the left channel, which is dead silent.

I’m happy to replace the remaining wiring and resistors in the right channel output stage, if these might be responsible. What about the other tube socket? Or, what parts could I swap with the other channel to see if the noise moves?

[denti alligator]

Unless you think it’s a waste of time, I will swap these parts from one channel to the other to see if the noise moves: .15ohm resistors on 4-pin socket, .1uf. Capacitor (4U to 7U), 220ohm resistor (A3 to 4U).

Should I replace the wiring near the R channel 4-pin socket?

[Thermioniclife]

How about you swap output transformers.

[denti alligator]

How about you swap output transformers.

I may do that just to rule them out. I mean, it has to be coming from somewhere, and it’s not in the left channel. Having replaced most of the output stage of the right channel I might as well keep going.

[2wo]

It does sound like you have come to the point of swapping transformer or other major components. If nothing else it gives you a chance to scrutinize each wire for something like a break under the insulation or something insidious, hold it in your hand and able to look from all angles.

And sometimes just taking it apart and putting it back together can make it magically start to work; gotta believe in magic...John

[Paul Joppa]

This is a tough one! I've been following the thread, but I'm not as familiar with the layout of the 2.0 so I've not been posting.

I can't say I remember every trial that's been made, but it seems the noise is determined to be in the output stage or power supply. It occurs to me that the power supply is "pseudo dual mono," that is there are two stages of RC filter for each tube (130 ohm/100uF). You should be able to swap the power supply outputs between channels to test them.

I think you've already tried swapping speakers, in case it's a fault in one of them or the cables or connections. But I may be mis-remembering, so worth a try if you haven't.

[denti alligator]

This is a tough one! I've been following the thread, but I'm not as familiar with the layout of the 2.0 so I've not been posting.

I can't say I remember every trial that's been made, but it seems the noise is determined to be in the output stage or power supply. It occurs to me that the power supply is "pseudo dual mono," that is there are two stages of RC filter for each tube (130 ohm/100uF). You should be able to swap the power supply outputs between channels to test them.

I think you've already tried swapping speakers, in case it's a fault in one of them or the cables or connections. But I may be mis-remembering, so worth a try if you haven't.

Thanks, Paul. I have tried swapping speakers. Even tried different speakers to be doubly sure.

I’m not following you on the RC filter: how would I swap the power supply outputs between channels?

[denti alligator]

Changed the misleading subject heading of this thread, since the left channel issue was resolved early on.

Yesterday I swapped out the 0.15ohm 3W resistors. Noise still in R channel.

Today I'm going to swap the 0.1uf 630V cap on 4U/7U and 14U/17U and the 220ohm resistor on A3/4U and D3/17U.

After that I guess I'll swap the transformers.

What else is in the path that I could check?

[Paul Joppa]

Thanks, Paul. I have tried swapping speakers. Even tried different speakers to be doubly sure.

I’m not following you on the RC filter: how would I swap the power supply outputs between channels?

I'll get back to you, but it will take me a while since I don't know the v.2.0 layout well.

[Doc B.]

There is a blue wire coming off each plate choke that eventually connects to pin 2 of one of the 2A3s. One side side it is attached at 1L. On the other side it is attached at 20L. Just swap the blue wires connected at those terminals. I'm guessing you may need jumpers/clip leads. Be very careful not to short the jumper connections to anything.

[denti alligator]

Thanks, Dan! Too late, though. I already removed both transformers. Oh well, fun times. I'm really, really hoping the noise travels channels, otherwise I feel like we've hit a dead end. Fingers crossed.

[Doc B.]

Might as well do both. Swapping output transformers will tell you if the output transformer or its connections are making noise. Swapping the final power supply nodes will tell you if the noise is coming from the power supply filter components that are unique to a channel. I would lean towards the power supply final node being more a likely culprit than the OT.