lost sound in right tube mono

While listening,the right monoblock dropped out.One slight pop and is was gone.
fuse is good
tubes all test fine
With the amps powered down I read the correct resistance at the pots(10 ohms)but powered on I read no voltage at the pots.The filaments in the tubes are working(glowing)so the tubes are powered up.
Looking inside no burnt resistors or anything obvious.
Thanks for any replies