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KT150s in Audio Research Reference 75 (non SE)

Hey all.  Need some advice. 
I've just dropped in KT150s into my Ref 75 (non SE). 

I purchased "perfect pairs" from TheTubeStore.  

I cannot bias them.  They are all too hot.  There are a couple (of the 4) that if I turn the bias pot all they way down will get very close to the bias range (per the needles).  There are another two that even with the pot turned all the way down are reading past the bias range and the needles are about 7mm beyond the bias range. 

Two questions:
1) Am I doing something wrong?
2) Will it hurt anything to run this a little over the ideal bias range, or just shorten the tube life?  Will it impact sound? 

I thought KT150s were drop in for KT120s.  Am I wrong? 

Thanks!

jo1mtb
jo1mtb OP
119 posts
 
By the way.  I dropped a set of Audio Research sourced KT150s, no problem, they biased w/ ease. 


joecasey
484 posts
 
By the way.  I dropped a set of Audio Research sourced KT150s, no problem, they biased w/ ease.
How do they compare to KT120s?
sewolla
8 posts
 
Just saw and thought I’d add my experience to the mix here.
I picked up a used Ref 75 from my local ARC dealer about 2 months ago. I was told at the time that it has a lot of hours on it, and that a fresh set of tubes would be a good idea, and that it would be a good idea to make the switch to running KT150’s.
I felt uncomfortable about just swapping out the tubes, without doing the full SE upgrade, so I did not do it.
A little while later it blew a fuse, so I took it back to the shop I bought it from to see if it was indeed just the fuse, or something else. When I got down there we had a great conversation about upgrading to the SE version or just switching to KT150’s. They recommended a call to George Meyer the local ARC service center, to get their input on it.
So that’s what I did. George Meyer’s tech was great. He said that yes indeed, just switching to the KT150’s was a good improvement to make.
So I did. George Meyer put in the new KT150’s, and found the cause of my amp’s blowing the fuse. To say they did a great job would be to make a real understatement. Fantastic service. It was done and ready to go in less than a week. Of course the amp just sounds fabulous.
So bottom line is, since ARC's  LA service center recommend the switch to KT150’s, without going the full SE upgrade path, I see no reason not to do it. George Meyer is an authorized ARC service center, and I certainly trust them.  Hope this helps.






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