[Amps] 3-500z(G)

[Gene Bigham]

It is my understanding that the 3-500Z and now the heavier anode 3-500ZG's need to be run red to dull orange at times for the very reason you stated, so the getter can work.  Perhaps it is not the color of the anode but the coating on the cathode which can be depleted and the lighter sweep tubes if run that hot use up their coating much more quickly than the transmitting tube which is designed for high temperature service.  I remember taking weak, soft 6lq6's and applying higher filament voltage for a short time with a tube tester to get them to come back to life by "boiling some more emissive material to the surface of the filament" sometimes, this was a very temporary fix.