Roland BOLT-60 hum on standby

[imacky]

My old Roland BOLT-60 has been sitting in the BR closet for years. I finally got it out, cleaned it up and and plugged it in. It powers on, but when I wait 20 or so seconds (like the manual says) and flip the standby switch there's a 60Hz hum, which none of the pots affects at all. It stays humming no matter how long it's left on (with standby on). This is plugged into a house circuit that's grounded properly.

I know nothing about tubes but I'm guessing one or both power tubes has gone bad. Is there any way to be sure? Is there anything else that would cause this? I don't want to put in a new matched pair of 6L6GC tubes and have it make no difference. Everything else seems OK.

Sorry for the lame n00b question and I hope this isn't a dup I've done a lot of searching for an answer already but not found anything helpful, and now the more I read/watch the more confused I get.

[sluckey]

Tubes don't go bad from just sitting around in a closet. But filter caps do.

[Stevem]

I have had this problem many times with amp brought to me.
The cure is replacing the the first filter cap after the rectifiers , but really all of the filter caps in the power supply should get replaced.

[imacky]

Thank you all; I will try the caps and report the result.