I've tested hundreds of picture tubes, but never run into this before.....

This picture tube is a 16WP4, in a Philco 51-T1607.

On setup, you set the G1 voltage at 45 volts, then turn the knob to increase the G2 cutoff voltage.....you turn the knob until it increases by two small divisions.

This Philco tube, I crank it all the way over, and it never increases. Yet, the tube tests good with the G2 cutoff cranked all the way.

The question is, is this tube good? :dunno:

I think I've had tubes do that on my 466 and still work, but it has been a while since I've seen that. I'd check for a purple glow in the neck to make sure it is not gassy.

I am used to seeing that G2 control behavior with weak CRTs (on a B&K 466 or 467), but then they do not test good either. These are tubes that are known-weak, and I usually rejuvenate them. Then, I often get "proper" behavior of the G2 control (and a good test reading too).

People here have mentioned "good cutoff" separately from "testing good or "good emissions" when describing good CRTs they have; I have never understood what it means, but maybe it is referring to proper results from that control? (If that is true, then maybe you have a CRT with "good emissions" but "poor/bad cutoff"?)

Kinda begs the question, what exactly IS cutoff?

Kinda begs the question, what exactly IS cutoff?

The Grid 1 or Cathode voltage that extinguishes the beam.

However, since CRT testers do not actually light up the CRT, they just make a guess, which brings back the fact that only reliable test for a CRT is what kind of a picture it makes!