oldest tube(s) in your system

I have a set of Wurlitzer amps that were modified to run a pair of 45s. The ones I've been using are pre-war but I don't know how old. They run fine. Those amps are no longer in my system, having been replaced by a single amp of similar power that is much more compact. It uses EL95s from the 1960s.

Yea, I figure 45 or 2A3 or similar would be about the oldest tube type still heating listening spaces.  Funny that as those are power tubes; would've thought signal tubes would be more likely to be oldest still in use.  All of our power tubes are new production babies.  And all of our signal tubes are older than me!

A pair of 45's in the Will Vincent Audio West SET45 amp. Along with a pair of 6C6 pentodes as input/driver tubes. Rectifier is a 5V4. The amp is built on a white powder-coated Dynaco ST70 chassis.

National Union 45's from the 1940's in my Supratek SET / 6SN7 preamp. 

I have no idea how old are the tubes in my system.  The amp and line stage run Western Electric 348, 349 and 310a, 310b tubes which were around from the 1940's through the early 1960's.  The 348's and 349's are extremely rare.