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AUDIO FORUMS >> Replacement Tubes >> 6922 Tubes - Replace as matched sets?
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Message started by Andrew77 on 12/13/21 at 23:56:15

Title: 6922 Tubes - Replace as matched sets?
Post by Andrew77 on 12/13/21 at 23:56:15

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

Title: Re: 6922 Tubes - Replace as matched sets?
Post by Archie on 12/14/21 at 00:31:47

When I have anomalies with my ZMA (or other preamps) I often end up swapping tubes around until I find a tube that the problem follows. Just replacing all the tubes might make the most sense but I'm poor and I find that sometimes a single tube just fails. Most recently I've had two separate output tubes fail in two different quads (well used). In those cases the bad tube was easy to spot since it was sparking inside! That said, when I examine the tube I can't see anything wrong inside.

Title: Re: 6922 Tubes - Replace as matched sets?
Post by __Jon__ on 12/14/21 at 02:30:29

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.

Title: Re: 6922 Tubes - Replace as matched sets?
Post by CAJames on 12/14/21 at 03:06:10

My experience is the best way to troubleshoot tube problems is to move them around and see if the trouble follows the tube. And sometimes just reseating a tube is enough to make trouble go away, at least for awhile.

As for replacing with a matched pair vs. a single tube I would say that ideally yes, you are better off with a new matched pair. But, again just my experience so FWIW/YMMV, I don't recall ever noticing any sort of issue when just replacing a single input tube. Power tubes are a (potentially) different story.

Title: Re: 6922 Tubes - Replace as matched sets?
Post by Andrew77 on 12/15/21 at 23:59:52

Thank you everyone for sharing your experience on this. :)