Ringing Sound In Tube Gear

The others have hinted at this, but tubes can be microphonic. The glass shell can vibrate with the sound in the room and this can get amplified again. Some brands or types of tubes are worse than others in this regard. Normally one would expect any problem to increase with playback volume.

An easy test is to tap very lightly on a tube with a pencil and see if you hear anything through the speakers. If so, tube dampers can help with this issue.

Is the ringing coming from one channel or both? If one channel try swithcing the tubes to the opposing channel and see if the ringing moves.

Do you hear it in both channels? If so for it to be a tube it would most likely be one that services both channels. I'm not familar with your amp but a single tube serving two channels is not uncommon, they have two sections.

Ringing is most often associated with the small tubes, try them first.

In my experience ringing in power tubes is not common except for a headphone amp I use :-), so it is possible, but again it would usually appear in only one channel.

According to the specs I found, that unit has:

Tube Compliment:

4 X EL34
2 X 6SN7
2 X 6922
2 X 12AT7
2 X 12AX7

It's probably not the EL34's or the 6SN7's. It's more than likely one of the 6922/12AT7/12AX7. I'm not sure how Onix uses these tubes in the circuit, so it's kind of hard to pin-point the culprit. I agree with tapping each tube with a pencil eraser lightly to see if you can find the noisy tube. Wow, that unit sure uses alot of tubes...

Tubes with long plates tend to be more microphonic. With the system on and at idle you can tap on each tube with a pencil or you can tap on each tube with your fingernail to locate the microphonic tube or tubes. I have heard of microphonic output tubes, so be sure to check all tubes.

Be very careful and diligent with precious tubes...isolate them from harsh vibration and nurture them like sweet little gentle babies. Be nice to them. Except for the tubes in the 147 guitar and bass amps I've dragged all over the world since 1967.