Last week I started getting some hissing and squealing from my left channel of a Torii MKIV that is 6 months old, purchased new.  Not sure it's the only problem, but I identified the input tube on that channel to have a problem.  Should I replace as a matched set, or is that only critical for output tubes?

How did I determine input tube was in need of replacement?  I had examined each of the tubes while in operation.  Looking for irregularities or differences in color and temperature.  After some research I was directed to very lightly tap the tube.  When I tapped the 6922 input tube on the left channel I got distinct sounds from the speaker.  Everything other rube that was tapped had no distinguishable difference.   I removed the tube to inspect and one of the connections from the pin to a lead wire looks suspect.  None of the pins are loose.

I plan to purchase the direct replacement(s) from Decware.  Any other options I should consider?  I am not looking to drastically alter the sound of my amp yet, I'm very happy with the setup and focusing on improving the room conditions for the first couple years.

Finally, any additional help / documentation on troubleshooting tubes, I am very interested.  I was not expecting the first tubes to replace would be input tubes.

Thank you,
Andrew

I also don’t have a firm grasp on what situations require perfectly balanced tubes and to what degree matching matters in the various circuits. Some places I’ve read said 10-20% difference is ok in driver tubes (which seems kind of not matched to me).  I have always tried to acquire tubes that are well matched and as balanced as possible, but it would be nice to know if / when tight matching isn’t as important. I suspect Steve would give a helpful recommendation for your situation,  if asked.

Thank you everyone for sharing your experience on this.