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Tubes, Mesa Walkabout and an old thomas organ

So i have an old tube organ that needs new power tubes. I just bought a walkabout combo and want to mess around with different preamp tubes. I was thinking of pulling some of the preamp tubes from the organ and using them but im not sure how to tell if the tubes are usable or garbage. Anyone got some advice on the situation?

-Mike
 
Pre tubes are basically triodes. Different ones have different voltages and you could
damage your amp using the wrong ones. You can cross reference tubes on line to find
which are compatible with the ones you want to replace but don't imagine just cause they fit the base, they're the same.
 
I guess I should have said that the walkabout uses 2 12ax7 tubes and so does the organ so I should be able to do a switch without any problems right?

Also, has anyone ever heard of " GE Electronic Tubes" or "Realistic Lifetime tubes". Thats what the organ has. Both are USA made and both seem to be working.
 
Having done a whole lot of tube rolling with my Walkabout, feel free to try any 12ax7, 7025, 5751 or ecc83's you come across and figure which one works best for your ears. While there wasn't a huge amount of difference in all of the NOS tubes I tried, I liked a Raytheon 5751 for the v1 slot and a GE 12ax7WA for the v2. You really can't go wrong with your tube choice (provided it is compatible) so long as it isn't dead and you'd know pretty quickly if your pre-amp tube was bad.