21fbp22 crt life

[miniman82]

Emission merely shows the amount of electrons given of by the cathode, in order to get some idea of the life left you do the 'life test'. For testers without this function, simply turn down the filament voltage to 5 or so. If the meter dips into the red, you'll know it's got a lot of hours on it but will still likely give a decent picture. Most of the tubes I have retain full emission all the way down to 4 volts on the heaters, meaning they have seen very little use. It takes a little bit of experience to get a feel for how your meter will respond to good and bad tubes, but once you test a few of them you get the hang of it. Take a good one and a weak one, play with the filament voltage while reading emission on the scale. You'll quickly see the difference in the how needle reacts.