Mcintosh tube amp MC 2301 - detecting bad tube?

[Elftrader]

I keep getting blinking red lights on my 2301 mac amplifier and hear it's probably due to a bad tube. How do I figure out which tube is bad? Or should I just replace them all, which would be very costly.

 

[Another Johnson]

1. Double check to make sure you don’t have a short across any of the output terminals (like a stray strand of speaker wire). Check at both the amp and the speaker.

2. If it’s not an intermittent short at the output, it is probably a bad tube. If all 8 KT88s were installed at the same time, it would be a good idea to replace them all. If you have a pair of 2301s and one is not misbehaving, swap the tubes one at a time amp to amp. This is tedious because you have to unpower and allow cooling for each swap. But when the problem moves to the other amp, you know you’ve found the bad tube.

3. You could buy a tube tester and test them.

4. The 12AT7s typically have a longer life, but you can swap them amp to amp too if needed to check them too.

5. If it’s been a few years, tube replacement is necessary maintenance and should be expected by tube aficionados. Doing them all at once freshens the whole sound. But first, be sure you don’t have strand of speaker wire intermittently arcing.

 

[Elftrader]

Thanks for explanation. I replaced one tube on one side of one of the amps and the problem seems to have gone away. This is a fairly new amp. So I hope all these tubes will last for quite a while at this point.

 

[Another Johnson]

Thanks for explanation. I replaced one tube on one side of one of the amps and the problem seems to have gone away. This is a fairly new amp. So I hope all these tubes will last for quite a while at this point.

That’s great!
If the tubes are relatively new, replacing one at a time is cost effective if, as in the case of the 2301, tube matching isn’t critical. You probably won’t have to replace another for a good while.
Enjoy!