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Tube amp down, need guidance from the experienced

I listened to my McIntosh MC275 Mk.IV all day yesterday without issues, as usual. Today I turned it on and left the room. Didn't pay attention at startup. Ten minutes later I realized it was not on. Eventually I figured the fuse had been blown, and replaced it. Turned it on again and found one KT88 was not glowing and cold. The rest of the tubes, both small signal tubes and KT88, were all on. Didn't attempt to play anything, turned it off, and here I am.

Obviously I need to replace the KT88, preferrably all of them. Unfortunately I don't have any spares on hand. What I'm anxious about, though, is to figure out if anything else was damaged. Is there reason to believe something else might have been damaged when this tube went off? First time a tube fails for me, and have seen a number of horror stories told on the net.

Thanks much!
lewinskih01
newbee
4,768 posts
 
Before you decide which tube to use, consider it's reputation, in general, for the tone it will produce (with your equipment - it is about synergy). I think the Gold Lion Genelex is an excellent place to start if you really don't want/need something specific in a tube, that is a tonal color to match your speakers and the rest of your stuff.

FWIW I've never used your Mac. I assume that it can use other tubes in the 6550/KT88/KT90 (and maybe KT120) family of tubes. If that is so, you have a lot of tubes to consider which can help you achieve a tone to match your system.
jedinite24's avatar
jedinite24
1,503 posts
 
My favorite KT88/6550 tubes are the old stock GE JAN Solid Plate 6550 tubes. Another favorite are old stock Sylvania grey plate 6550 tubes. A recent production KT88 tube that I like was the solid black plate Penta Labs KT88 tubes.
lewinskih01 OP
909 posts
 
I thought I should give you guys feedback after all your help: I installed a KT88 in place of the failed tube, played the system for an hour, and everything seems to be as usual. Thank goodness!!

Beyond the anxiety the tube failure created, this thread was most helpful to me in that I learnt several things. Great forum, great answers, thank you!!

So now I'm running my amp with 3 tubes that have 5 to 6k hours...I need to replace them ASAP. After the reading and exchanging with Jim McShane, I'll go with new Gold Lions.
knghifi
1,668 posts
 
So now I'm running my amp with 3 tubes that have 5 to 6k hours...
I've never heard KT88 last this long. Either you are VERY lucky or miscalculated.

My old amp uses matched quads per mono. The sound was getting weak, several tubes just stopped glowing and died peacefully ~2500 hours.

I never had any 6550 blowing but several reissued Gold Lion KT88s failed and took out resistors only after several hundreds of hours of use.

If I were you, check out KT120 ... only heard positive comments in terms of sound and durability and NOT just more power.
czarivey
5,946 posts
 
If there was lots of idle time, I guess the number of hours increas drastically. 5...6000hrs is darn lot. I'd never idle tubes and always would turn them off when not listening. It takes only 10m for tube to reach normal DC offset.
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