MC-60 tube replacement?

I had a 6550 blow up yesterday and there's a '27' written on it by the guy who rebuilt them. Each power tube has a different bias number written on it.

What do I need to do? I can't imagine bringing the amps back in every time they need a tube??

Thanks much~

 

Replace both with matched pairs.

 

yep, agree with Pio1980. Also don't forget to check the audio coupling cap to make sure its not leaking DC.

am also assuming you have updated the bias rectifier in the amp. If not, would do that before inserting a new pair of tubes.

good luck.

 

Thanks guys...I'm not sure what was done. The other tubes have numbers like 30, 32 and 29 written on them....so I can just buy any matched set?

 

you can try to match up a single with your non blown tube, but can be tough since you really dont know how many hours are on the tubes.

a pair of 6550 or KT88s are not too pricy so would still recommend that option.
But before you do anything, would suggest you check your coupling caps for leakage and replace the bias supply. Otherwise you will stick in your new tubes and run the risk of smoking your new tubes......If you dont have a variac, make a dim bulb tester so you dont draw too much current and take some DC measurements on the coupling caps. One side should show high DC, and the other side none.

 

Matched tubes aren't necessary in the unity coupled circuit. There's no harm in using them though.