KT-150 Tubes- Push Farther or Replace?

@welcher - that is really unfortunate and a little suspicious. I haven’t heard a Ref 75SE with KT-150’s, how has the presentation changed for you since moving to that tube?
 

@decooney- Thank you for the suggestions sent. After noting the previous bias levels I moved the tube in question two times and the problem followed the tube. I guess it’s just a bad apple! What’s interesting is that although all of the tubes had factory measurements written at the base this problem tube was the only one w/o a slot number noted on it. I moved it to where it shares the bias adjustment with the next weakest tube and was able to get that pair to within range. If this holds up I will continue their use to see how far they can go before becoming unbearable.

With all that is going on now with availability I didn’t want to jump to a full changeout but as @russ69 noted I don’t think it will be too much longer.

Thanks Again!

@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!)

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.

@mulveling- I hear you and thanks for the warning. My curiosity was driving my actions on this one- I had to know how long they would last. This confirmed that the recommended usage time of 2K hrs was accurate and from what I’ve learned here I’ll probably replace them at 1700-1800 hrs going forward. Anyway, I replaced the entire set earlier this evening and it’s all good! 

@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.

@elliottbnewcombjr -

thanks for the response- I’ll send you a pm with the short list of tubes

After a little reading and putting some more thought into this I’m realizing the reality of this (at least my reality!). As @mulveling first suggested- my system uses 4 different makes of tubes. A gang of 8 KT150 and 11 6H30’s. My DAC uses a couple of the smaller 12AT7’s (which seem to go on forever). With this commonality across the equipment I don’t really see myself critiquing individual tubes as opposed to wholesale changeouts when approaching the recommended end of life hours.

It also seems (pointed out by @mulveling ​​​​@invalid) that a tester really isn’t going to buy me much when it comes to the KT150 in particular due to the voltages required for an accurate test/comparison. The test stations equipped to deal with these are of considerable expense (more than a new set of tubes) and in reality I would just pull and replace.

I liked the thought of having one though- kind of nostalgic but (at least in my case) it doesn’t seem like I would put one to much use. As always- I appreciate the advise given!

@elliottbnewcombjr-

Hello! I can't speak to which testers would be considered real or better than others- I just did some quick reading on the products suggested by others. Those were the Maxipreamp, Amplitrex and Space-Tech Labs. It seems there are many out there in the used market that ranged from $750 on up and new units going upwards of $1.5K (or more). I have no past experience with these as my amplifiers bias adjustment is performed while reading the meters on front of the amp.