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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.

designsfx
decooney
2,102 posts
 

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.

russ69's avatar
russ69
3,520 posts
 

Not holding bias is a clue that those tubes are done. Time to replace. 

welcher's avatar
welcher
117 posts
 

I agree with @russ69; I had to recently replace 1 Kt150 in my Ref 75SE because it would not hold bias after 400 hours of use.

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