Replacing tubes on used equipment bought on A'gon

Depends on type of tube. Tubes degrade gradually with use, but will "work" considerably longer than their ideal useage time. So you could have a tube working 5-10 years that musically degraded after 2-3 years. The only way to know is to try new tubes and see if you hear a difference. If not, you have a back up set of tubes.

I would find out what the manufacturer requires for stock tubes and purchase a set for each. This way you'll have a good idea of the voiceing intended. From there you can descide for yourself whether its worth the tube rolling or not...Have fun !