I've had real good luck restoring cathode emission in TEK manufactured CRTs. A number of testers intended for the TV repair market can do this: the gold standard is the Sencore CR7000, but the Sencore CR70, as well as testers from Beltron, Heathkit, etc. also work well. You want the type of tester that uses a current limited supply to pull current between the cathode and G1 of the CRT, not the type of tester that applies a high energy pulse to the cathode. The current limited type of operation is usually referred to as cleaning or restoration as opposed to rejuvenation. Scope tubes, with their small structures, call for careful work with short duration, but I've had close to 100% success, including tubes that were so dim the trace could barely be seen in a totally dark room.
This process takes some finesse, so I would not start learning on a precious tube - If you happen to know anyone who used to work on CRT TVs, or someone who is into arcade games, they may be able to help, or point you to someone who can.
Good luck here. Bottom line: this technique is always worth trying on a weak tube - after all, you have nothing to lose.
Regards - Kurt