pre amp hiss from 1 channel

[Mordante]

Recently I noticed that I have a hiss on one of my channels. After testing it became clear it comes from my tube pre amp, an Octave Phono Module.

The pre amp has the following tubes.

1) ECC88/6922 tube in the XLR direct drive output module
2) ECC83/12AX7 Input tube
3) ECC81/12AT7 main amplification
4) ECC88/6922 output buffer

Since all of these tubes are used as stereo tubes, one tube for both channels I'm not sure which tube I should replace or check first.

Edit1:

The is hiss is not affected by volume. When the volume is set to zero it's there and the same when at 10. It doesn't get louder of softer.


(wish I could post pics on this forum directly without the need to look for a place that lets me share them, I used to use Facebook for this but I don't think it allows sharing any more).

 

[jadedavid]

Not having the schematic to know exactly how the tubes are used in the circuit, the least expensive way would be to obtain one of each type of tube (I.E. one 12ax7, one 12at7 & one 6922) and simply use the new tube to replace an existing tube one at a time until you discover the culprit.. Kind of labor intensive but will get the job done.

 

[Mordante]

So I found the faulty tube, it was the Gold Lion Genelex ECC88/6922 tube in the XLR direct drive output module. I replaced it with the stock tube which came with the amp.

Anyone some ideas what would be a good tube for this location in my amp?