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 The Ref 75SE comes with KT150's. I have not tried any other tube types.

@welcher- for some reason I thought the 75’s used KT-88 or 120’s, maybe those were the older models? (Or I may be just completely off base!)

@designsfx The Ref 75 came with KT120's while the Ref 75SE came with KT 150s

Got it!  I remember reading many posts some time ago where people were wondering whether that tube was compatible with amps designed for use with KT120’s. I was not aware that ARC had made the change. Thanks for the clarification on that- I bet it sounds great.

@elliottbnewcombjr - That sounds like good advice. Are there specific units you've had experience with for home use? BTY- the tubes I have are wasted! Stubborn me! I thought I'd try to see how far they could go but it's to the point where they won't hold adjustments made for even a day. A new set is going in tonight.