Do I need new tubes?

[fome]

Today, I came home to find that my amp plays at a much lower volume than normal, and has a strange crackly kind of breakup when I play hard. When I checked the tubes, I discovered that one of my power amp tubes is glowing much brighter than normal, like it is glowing red-orange in the middle plate. Time for a retubing?

 

[dmt]

Immediately! That one tube is drawing too much current and "red-plating'. Very bad. Do NOT use the amp until you replace the tubes with a fresh set. If it still red plates with a new set of tubes take it to a tech and have him check the bias and grid resistors. Make sure you retube all of the power tubes, dont get cheapo here. The pre amp tubes should be fine and do not need to be replaced. Those typically last for a lot longer. Don't let some tech sell you a new set of preamp tubes that don't need replacing.

 

[fome]

Ok, I replaced the power tubes, but the new tube is red-plating too. I have to take it to a tech...

 

[acorkos]

just to truly rule out bad tubes (original and replacement), swap the one that was redplating with one of the tubes next to it....if the same socket causes the swapped tube to redplate, you've got a problem on the socket....it's likely the pins just need tightening, or you may have a bad resistor associated with that socket.

 

[fome]

I got my amp fixed by my tech in one day. Turned out that one of the phase inverters went bad, causing there to be no bias for one of the tubes. Thanks for the help guys.