I have a crt from a 1955 RCA 21s548. It tested strong, but for the life of me I cannot remember what CRT it is. It has a sylvania label but no number. It used to be on the cab which is now gone. DOH! I was hoping it would cross for another set ...but. whoops. It's a 21" by the way.

According to my Beitmans for 1955, it's a 21ZP4A or 21ZP4B.

Thanks! I just picked up my 55 stromberg Carlson and it has a 21aup4. It's still in the jeep. Tomorrow I am going to unload and test it. I hope it's good because I don't think the 21zp4a , or my 21yp4a would work in it. Unless someone thinks otherwise.

A 21ZP4 or 21YP4 will not sub for a 21AUP4. All three are 21 in, 70 degree, but the bulbs are different shapes and the 21Z/Y have slightly smaller screen sizes. Don

I didn't think so. Well it looks like the rain finally stopped so I should get that tv in the garage and check it out.