The above advise is good... If you find one of the 6922s is bad, make sure you do (or have done) a calibration of the gain stage. This is different than setting the bias, which should also be done if there are any of the tubes replaced. At minimum, you will need a good digital volt meter (DVM) (3 1/2 digits or better) with appropriate leads, the procedure for gain stage alignment, a parts list, tube electronics knowledge, small flat-blade pot. adjustment tool, and about 2 hours time. To adjust the bias, you will only need a DVM, and the adjustment tool.
I have done this procedure, and it yielded good results both sonically, and it reduced the amount of heat the amp was producing.
As for the tubes, ARCs tubes are best, since they are properly selected and matched. I have used others, but make sure you have spares if you are calibrating your amp.
BTW, if this is amp is more than 3 years old, and you listen frequently, chances are you may want to replace all of the tubes and do the above alignments. E-MAIL me if you would like to discuss this further.
I have done this procedure, and it yielded good results both sonically, and it reduced the amount of heat the amp was producing.
As for the tubes, ARCs tubes are best, since they are properly selected and matched. I have used others, but make sure you have spares if you are calibrating your amp.
BTW, if this is amp is more than 3 years old, and you listen frequently, chances are you may want to replace all of the tubes and do the above alignments. E-MAIL me if you would like to discuss this further.