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Zenith liked to use them on their mid 60's - early 70's tube sets. They seemed to use them for several purposes in the horiz. sweep circuit. I remember some 16" - 19" B&W portables where the neon bulb lit up constantly when the set was on. I have a 25CC50 chassis color set that uses two in series in the HV regulator circuit. They light for a few seconds after the horiz. sweep starts then go out once the HV comes up.
Mike