Re-tubing a McIntosh power amp

Heavy - your post seemed heavy on buying in bulk and sifting thru the crapshoot of grading tubes. You should get to know Andy and his ears and test gear. I am sure he would enjoy a conversation with you.

Mac in the golden age designed for tube longevity, my 1960 MC240 ran hard for most of it’s life has all original small signal tubes, ditto the 1965 MX110z save one ! tube replacement about 6 years ago.

power output tubes a different story but still relatively long lived in a Mac…. Remember the performance clinics run by factory techs at the dealers ????
Fun

re-reading your initial post, it seems like you, after reading, are concerned about ’probable failure’, and don’t want to ’wait and see’.

I get that, I always want a spare set handy, and I understand staying with KT88’s, seems wise.

So, what ’non-exotic’ RELIABLE KT88’s? It’s a simple question really.

I went JJ KT88 Blue Glass. Blue glass is just a different colored glass, just for looks, (mine are very visible), identical to their regular KT88. I’ve never had issues with JJ. My Electro harmonix 6550eh’s now my spares, maybe I’ll need them, after say 5,000 hrs playing time, for me 15 hrs/week that’s 6-1/2 years. Professional use in a guitar amp is a whole different thing.

But, like anyone, anywhere, you can find ..., i.e. from ghosthouse, a member here posted in 2007 had nothing but trouble with JJ

https://forum.audiogon.com/discussions/expected-hours-for-jj-tesla-kt88

I did buy some Gold Lion Cryo Tubes once. Loose with birthday money, the difference is only .... WTH. I wouldn’t do that again. They are in an amp or the mono amps downstairs, I forget.

https://www.worthpoint.com/worthopedia/gold-lion-kt88-cryo-treated-matched-24909629

Also Roger Modjeski ( rip ) built some very advanced testing and grading gear for modern tubes - I have a set of his RAM KT.88 in my RM-9 and his super precise low noise driver ..

RAM tubes

RAM throws out or returns some 90%…. Sounds like the definition of crap shoot…

I played about with this a bit on my CJ Premier 11a.  Found the GL KT88s to be by far the best.  Don't know whether or not your amp allows individual tube biasing but if it does, it sure saves on not having to but matched tubes.