[Jeffhs]

Tube substitutions must never be done haphazardly. Putting tubes in the wrong sockets in a TV, radio or any kind of electronic equipment using vacuum tubes can have disastrous results; for example, the filament pins of one tube may well be the plate terminals of another, possibly causing circuit damage or worse (including but not limited to fire) if two or more tubes are put into incorrect sockets. I would never substitute one tube type for another unless I was absolutely certain the substitution would work. A good rule of thumb is to check a tube substitution manual if you are in doubt as to whether a particular substitute will operate properly. If you do not have such a manual, replace the tube with the same type already in the device you are servicing.