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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
jallen
502 posts
 
Replace both KT88 tubes and hopefully the fuse stopped further damage. You can take off the bottom cover and look for further damage. Call Mcintosh and get their opinion. With tubes many possibilities exist, not all good ones. Hopefully you were using fast blow fuses. Slow blow respond too slow. Jallen
hifigeek1
770 posts
 
The tube arced a resistor may be open. I suggest you contact the McIntosh service dept. for further assistance.
atmasphere's avatar
atmasphere
11,874 posts
 
I would just change the power tube and see if it works.

If so, then I would investigate perhaps replacing power tubes if they are getting weak. Arc-over failure is a common failure mode of weak power tubes.

If the amp does *not* work I would get the amp serviced. So you can approach this in a simple yes/no manner.
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