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OK, let me to recall. We learned that the “hysteresis” (for a lack of better world) manifest itself on used tube only. Also, what I see in the images the one of the half of the used tube has more “hysteresis” then other. I think it leads to the following considerations:

1) Your tester might have some kind of anomalies when it drive used tubes (highly unlikely)
2) This given used tube has the “hysteresis” anomaly because it was overheated by me during its service.
3) This given used tube has the “hysteresis” anomaly because it’s a Russian tune and everything imaginable might happen with it.
4) All used 6C33C has the “hysteresis” anomaly because it is a common behavior of exhausted 6C33C

Among all those cases the last one of the most valuable as it might present an objective testing opportunity about health of 6C33C. I think to confirm it would be necessary to run a few other used up 6C33C and to see of the “hysteresis” will be there. If you do not mind I would propose to send you a few other used 6C33C to see what happen. Interesting, Jim, can you elaborate more about how you think the “hysteresisation” of 6C33C might manifest itself sonically.

BTW, I use the shutting down method sometimes in my tube tester. While I measure cathode emission I drop filament voltage from 6.3v to 4V and I have observed that “fresher” tube has less emission degradation.

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