Try this link for a comprehensive listing of tubes:

http://tdsl.duncanamps.com/

There are two general factors in tube replacement (beyond having the correct pin base.)

The bigger factor is internal wiring - do two tubes have the same pin-out for the internal connections? A tube that has the heaters, plates, grids, etc. hooked to different pins simply will not work unless you rewire the tube socket.

However, even if the pin-out is the same, the other factor is the electrical characteristics need to be fairly similar for a tube substitute to work. You may or may not be able to substitute a tube if gains, current draw, circuit voltages, etc. are different.

As an example, I recently rebuilt a Dynaco ST-70 and used 6L6GC outputs instead of EL34s. I had to replace the 10K bias pot with a 25K unit in order to provide enough adjustment to bias the amp.