McIntosh MC275 VI preamp tubes

Why not buy exact replacements?  I may be counterculture in an audio forum but what’s wrong with the date you brought?

I can appreciate upgrading and I’m a history major. So I make engineers and scientists to achieve my goals. 
I have  MC 2600 preamp and I appreciate the impact of my preamp. I’d be more inclined to add a phono stage than change the phone tubes. After all that engineer is more trained than I. 
If I final a better preamp, I’d be happy to buy it and would rather upgrade than try to tweak myself to the same results 

Re-reading this. Small signal tubes last a long time. You sure your KT88s are not getting tired? I suspect they might need re-biasing, if not replacement. 

you may want to test the input tube for performance. As others have noted, they usually last quite a while. If you do not have a MC tester, some places offer testing for a reasonable price 

I bought 6sn7’s from Brent Jessee for my Cayin Integrated Amp. I always test new tubes when I receive them, they were good.

http://www.audiotubes.com/12ax7.htm

I did not like their sound.

He had me wait and listen after breaking them in (60 hrs), and if I still didn’t like them, return/exchange them. I paid shipping, bought less expensive tubes, they sound terrific, and got a full refund for the originals.

Make your best guess, buy from Brent, see if they sound good, Oh Happy Day, if not, try another.
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Do you have a tube tester?

they give you good clues, and confidence in existing and new ’matched’ tube sets. find problems, find non-problematic but weak(er) ones ..... I test all tubes annually prior to Thanksgiving, ready for the Holidays. They last a longgggggggg time.

My simple tester always agrees with my big one, I don’t bother with the big one any more. All 17 tubes of my McIntosh mx110z’s tuner/preamp tested good here. Audio Classics overhauled it, they didn’t replace any tubes, (surprising from past experience with others). That gives you more confidence in them as well as my tester.

Why not buy exact replacements? I may be counterculture in an audio forum but what’s wrong with the date you brought?

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Because anything is better than the current stock Mcintosh super cheap Chinese valves they sell at 100 times the price THEY paid.. Talk about CHEAP valves.. Under 5.00 each in bulk. 3.00 usd, is more likely.

But there are people in some countries trying to sell them for 2-4k. because of the 10.00 wooded box they come in, and the word Mcintosh burnt in the wood.. 300.00 usd worth of CHEAP valves at best.. JUNK..
The shipping cost more than the actual valves..

Regards..