The filament may be burned out? Operate the tube with 6 volts on the filament in your tester. After ten minutes see if the tube is warm?
Probably just time to go bad? This tube is used as a detector and nothing in a radio should cause it to go bad.
A 6H6 is dual diode detector. You could replace it with two germanium diodes. Don't use silicon. Voltage drop is too high.
Replacement tubes are available but if you don't have one 6AL5 can be used with an adapter.
Norm
:Hello I just tested all the tubes in the radio and the 6h6 tube will not show any needle movement on my tester. Never had a tube show absolutely nothing. Can this radio blow the tube? Is there anything I should check for? Or do I just have a burned out filament in this tube. I am not sure if i have a replacement either as I dont know what will substitute