KT-150 Tubes- Push Farther or Replace?
Hello All-
Seeking advice from others that may have been in this spot before. I’m currently running my trusty Audio Research GS-150 power amp and I’ve just crossed 2200 hours on this set of tubes. I have a new octet of KT-150’s waiting in the wings.
Within the last 200-300 listening hours I noticed that the bias was requiring adjustment after every 3-4 listening sessions. This seems to be driven by two of the tubes continually falling low in bias adjustment.
As the tube bias is slaved in pairs would/could it be beneficial to isolate the two tubes that keep falling low onto the same pair of sockets with the hope that bias can be more evenly maintained or does it just sound like it’s time for these to GO?
The amplifiers manual states that replacement should be around 2K hrs but I’ve read posts here stating 3K might be achievable. The current situation is lower quality bass response and weaker soundstage. Any thoughts would be appreciated.
Have you tried swapping out/in two other kt150 tubes from other sockets and compared? If the manual states 2000hrs, that could be averaged out over a series of tubes they’ve replaced and tested over time. Some +/- hundreds of hours difference for example. I’d try to figure out if its a condition isolated to those two tube sockets or just those two tubes first. Go from there. Or call them if you have not done so already. They may share other helpful self-tests you can do at home. |
Sounds like you've got it figured out. A while back I watched a tour of the factory and how they batch those groupings of matched kt150 tubes for your amp. I recall thinking I'd likely not get too hung up on keeping matched quads or octets if I owned that amp, and maybe just keeping a few matched pairs around and replace those pairs when needed. Hopefully you can replace them in some kind of way where you're not replacing all of them at once. Good luck with the bias checking and longevity! |
Agree with @invalid, some circuits are running up to 600V plate voltage at about 80 - 85 mA current per tube. I ran my KT150s in the 50ma range per tube and they still sound great. Some of the diy folks were talking about this a while back, getting up to 4,000 hours without issue, yet noting some of the older tubes had getters fading faster than more recent production past few years. Best to follow the rec above "best way to test is in the circuit". Keep a close eye on this 2nd set for a while and check how quickly they stabilize at their first bias set point. Best of luck. |
