Noisy Sunn Sonaro

[gbono]

Well performing amp except output has noise (see attached). The filter capacitors as well as other electrolytics have been replaced. If it's ripple from the supply than where is it getting in?

[The Dude]

I'd start by removing tubes, one at a time, and see if you can isolate the noise to a particular gain stage.

[gbono]

I haven't used this forum in awhile - where are the attachments that I posted?

[The Dude]

I can see them. Maybe refresh the page?

[gbono]

Okay thanks for pointing me to the obvious since I didn't believe the new Sovtek 12AX7 could be bad/noisy!! Replace it with a newish GT ECC83 and the waveform is gone - put the Sovtek back in and bingo noise is back.

[Enzo]

ANY tube can fail at ANY time. New is no guarantee a tube is good.

[The Dude]

Agree, especially these days. Tube QC isn't what it used to be.

[drewl]

Just an FYI, I've gotten someone else's rejects from New Sensor this past year, like a Burgera labelled tube in a Sovtek box.

I'm sure they probably had supply problems this past year like everyone else due to Covid-19.

[gbono]

What's the consensus on tube shields? Do they reduce power dissipation?

[The Dude]

In general, tube shields are just that- a shield. The purpose is to keep noise from radiating into the circuit. They also keep tubes from falling out. I don't see how they would effect power dissipation. They aren't normally used on output tubes, because they can trap heat, and because the signal level there is high enough that a tiny bit of noise won't be noticeable like it would be in an early preamp stage. You usually see tube clips of different varieties on the output tubes to keep them from falling out- not shields.

[g1]

I haven't used this forum in awhile - where are the attachments that I posted?

Do you see them now? If not, you need to change over to 'posts' mode (rather than 'latest activity') in your user settings under account tab (scroll down to 'conversation detail options').

[gbono]

THX G1 I refreshed and can see attachments,