Cutoff and Auto Restore on Sencore CR70

[Phil Nelson]

I have a 12LP4 CRT that seems pretty dead, but it never hurts to ask.

The tube had a crusty old brightener on it when acquired, so I didn't have high hopes in the first place. It initially tested at zero emission and I couldn't move the needle at all for the Cutoff test.

The first thing I tried was cooking it on the tester overnight at slightly elevated filament voltage, but the emission remained at zero.

I tried the Auto Restore function. During the three cycles, the needle moved only slightly above the bottom of the Current scale.

It still flunks the Cutoff test -- even turning the Cutoff control all the way clockwise doesn't move the needle at all. Following the Auto Restore, the emission moves well into the Good zone if I turn the Cutoff control all the way CW.

If I'm reading the manual correctly, the low (absent) cutoff means it may light up but have awful contrast.

Is it worth trying anything else, or should I write it off?

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html