Testing an old scope CRT

[Dan Schafer]

Hi All
I have a 3AP1/908-A to test & was wondering since that CRT has the heater & cathode connected together, will it test properly on my Heathkit IT-5230 CRT tester? I get the short lamp and the emission instantly goes to 6 without the normal slow warm-up rise & the cutoff control takes it to 1 when at minimum. I put a load resister across the filament to track it better for the needed 2.5V filament voltage.
Thanks in advance for anyone's 2 cents.
Danny in Cleveland