Got a 10BP4
 

I picked up an untested 10BP4 on ebay. I tested it with a B&K 465 and the emission is about 340, so I'm happy. The cut-off is supposed to be in the 30-60V range but it was 25volts. So, that might be a little weak. I can't beat the price though. I never thought I could get a good CRT for so little.

I think I understand what's happening here. If anyone knows for sure and can confirm, or correct me, please do so.

As g1 is biased more negative the effective aperture is reduced and the electrons getting through are now more from the tip of the cathode. In normal operation this would be the case and the tip would be the most critical part of the cathode and also get the most wear/aging. So, although it may have good emission it might still be a little weak.

This is intended to be a spare to replace the 10MP4 in the Sylvania I just purchased. I don't have the set yet but I didn't want to pass this up, just in case. I only have to add a 275 volt supply for g2. Otherwise, it's a drop-in replacement.

John Y.