CRT substitution reference?

[leadlike]

17AP4: none

21BSP4: 21ACP4, 21AMP4, 21CUP4

So says my Howard Sams tube sub book. If your 21BSP4 crosses over to the AMP4 series though, I know it will work with just about any 21" 50s tube with that degree of deflection. I used a 21CBP4 (to replace a 21amp4A) with some very minor mods to my set (basically taking out the focus magnets as they were no longer needed, putting centering rings onto the yoke).

I think you could make any number of 70 degree 17" tubes work, but I do know that there are some differences in the face curvature of some types, so your bezel may not fit properly. My tube manual shows a few that may be able to work, but the neck lengths are different, basing is different, etc. So it wouldn't be plug and play. If I get time today, I'll check into it.