Kt88 or 6550 tube for McIntosh MC275

A pair of pairs? LOL sounds funny. ME I'm picky.. I'd have to look at the way they auto bias. It's been a while. If I remember,  there was a reason I used quads in a 275, I think it was early break up. It's been 30 years ago.

I would still pick up quads for that 275. Match the signal valves too, pairs per rail. It uses like 12az7 right? match them in pairs and look at their position. preamp, signal, la-te-da. Put them in, that way.. L vs R (one pair)

I remember. To match the valves in my 60s if I wanted to use them and not have an issue, between the two. AND they will. I match left to right. I had a few problems with that. VERY sensitive, Klipsch La Scala, or Jensens speakers per say, show EVERY flaw, from higher floor noise, L/R, distortion, all kinds of crap, behind mismatched valves. Gotta be picky with the old stuff and the new for the BEST SQ.

Regards

I just posted a series of answers on this very topic last night.
6550=kt88

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One was designed in the US one was designed in the EU.

They physically look different, as does the KT 90 you reference also.

They are not the same, nor do they sound the same. ALL 3 differ in design, and vary from manufacture to boot.

6550 does not = KT88 and certainly not a KT90 valve, different all together again.

I read your findings, I had to wash my face with cool water and take a TUMS! Pure bla bla bla...

Please! You started a tube flipping business right... and paid 1500.00 for a pair of valves.

TUBE FLIPPING.  I admire you're stones... Mercy

VA, It's stands for Valves Anonymous. Might help. GA, Gamblers Any, AA, NA...

Regards

Is that an early MC275, or the later model? I notice a much greater difference in valves in the early model.

The preference to KT88 is because GREAT 6550s can break the bank.. 500-1000. a pair More than NOS KT88 GL

6550 GE TungSol, Old stock. That is a different sound than a KT88s

I like both, I have both Solvex and Golden Lyon (not my favorite). Good valves.

I have a few sets of 6550 GEs. I also found a Tube Tec valve that was pretty darn good.

I like the KT88, bottom to top, if the valve is going to be doing bass duty, too.

If it’s in a mid/highs, I use a 6550 GE. It’s just tough to beat that sound. It’s a little slim in the BASS department, but VERY smooth mids, and wonderful highs.
If you’re a vintage Klipsch, horn kind of guy.. They just do a great job with Macs, MC60s, and older 275s, sporting that valve, and Tellies/RCA for the signal valves.

Just so you know PSVANE makes a heck of a valve, over the last few years..Power and signal.. ShuGuang 6550s, are great valves also and without breaking the bank..

Very important to get matched valves with the old Macs, Yes it matters. Mac is different, not like anyone else... A Mac will show you every flaw in your system. Mismatch valves cause an early breakup, on the top especially. MATCH the valves...

Enjoy the sound..

Regards

oldhyvmec - don’t waste your breath!

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Well OP is getting 2 cents worth. I was glad to help, If I did, or not, I’m not sure. Golden Lyons? WOW. I picked up two matched sets of KT77 (sixtets), I had a set of NOS Volvo, Red Rubies, and EH fat bottle and Slim Jims EVERYONE outperformed the Golden Lyons.  I had failure to top it off, with the GL.

Golden Lyon are within 10%, the Red Rubies and both EH types were within 5%.. The GLs were 30-100% more expensive... ????

Solvex are great for the ol 275s, Better than JJs sonicly.

You know I noticed the post number 1000.
Quit the little chatterbox aren't I...
Now I need a raise, this job has some serious wage issues. :-)

Regards