Noise floor in a hybrid power amp - Left channel higher than the right

Is it normal for a hand-built hybrid power amp to have imbalances between the left and the right when it comes to noise floor?

I've tried swapping tubes between left and right channels and it's always the left channel having a higher noise floor compared to the right. The amp is built using a wooden chassis so the lack of shielding may have something to do with this, but if that's the case it should affect both sides more or less equally.

When I tested the power output, the two channels were within 5% of one another...and yet with nothing connected to the power amp other than the speakers, the noise is noticeably louder on the left. :/

 

It might be the tube. Or one side is closer to the transformer.

 

I had a similar experience when messing about with a yuan=jing TA2022 power amplifier module. For some reason the noise floor in the left channel was higher than the right. I decoupled the left input using the supplied inductors, never could figure out what was causing it. But my amp was only intended as an experiment for dirt cheap diy, so I was less concerned overall.

You might try this to identify some odd grounding pattern in the affected channel, isolating the cause will be a little more complicated.

.. dB

 

What is the noise character like? When it's hum, then it's likely picking up transformer.
Are gains bw the channels equal? If not, then negative feedback might be missing in one.
When it's hiss then upstream the input tube the culprit can be cooked VAS transistor, damaged current source transistor or as simple as too little quiescent current in output stage.

 

There are individual volume controls for each channel. If I turn the volume all the way down, the two channels are pretty much silent, except for the normal background noise one would expect from any solid state amp. This is in-line with what the amp designer told me, that turning the volume all the way down would = just noise from the SS portion.

I THINK I've traced it to a failing/failed new prod. tung-sol 6SN7 in the chain (my preamp also runs 6SN7s or 6SL7s. At the time of the test, I had two sets of 6SN7s running in the two amps and one pair was the tung-sol). This morning when I switched between 6SN7 and 6SL7s to determine the cause of the noise, upon plugging in the 6SN7 tung-sols, there was a really loud hum (kinda hum that you associate with a partially plugged in patch cable in a guitar amp) from one channel (though nothing seem to have blown in the tube). Swapping back in the 6SL7 eliminated the noise.

Thank you all for your replies. Cheers.