Are you sure all 8 are bad? Usually you only use 1 main pair and 1 or 2 inputs? Save you a few tubes that way.
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I assume you are looking for new production tubes, and something rugged and quiet (ARC's seem to like them best), and want something with a bit more warmth than Sovteks. My first choice would be EH6922's and, if you want a bit more color but not as balanced, the JJ's are OK too. I use them both, but neither in my ARC SP10 where I use NOS 6h23's.
Thank you to all. Actually, comparing to McIntosh C20 preamp, ARC LS22 ( I just bought) is lacking of high and low frequency. It is OK in term of noise ( I think it is better than Mc Intosh C20). So, I am not sure what causes the problems I hope replacing tubes will fix the problem! I am going to try some tubes and let you guys know the results. Feel free to recommend.
You need the manual or schematics usually. AR will help if you call them. You need a pair of tubes for the gain stage (Most likely the pair closest to the outputs) and a pair for each input. The sockets should be labeled in some way such as v1, v2, v3 and so on.
If you only use cd, you only need 4 tubes.
Ls22 has a pair of input tubes then 2 pairs of voltage gain tubes then a pair of Cathode Followers. The tubes have 2 channels per se and the Balanced uses both for a extra 6db of gain vs the unbalanced inputs.
So V1 and V2 are most important to be quiet and have the sound you like and V3-V6 will increase the gain and shape the sound some more. And maybe someone can learn me on what is important about the Cathode Follower positions.......
Jiceman, FWIW in my SP10 I used 6h23s (low noise/rugged) in the critical positions but I found I can put 'colored' tubes in the cathode follower positions (which do not add any gain and are less demanding on noise issues). I long ago gave up trying to get tone from the critical positions.
The cathode follower tube/circuit provides no gain but affects the output so that you can drive long runs of IC's. Google it - I'm sure there are many thorough explanations there.