Hello,
Last weekend at the WARCI , Milwaukee swap meet I saw this crt in the rear of a seller's van. It had no numbers on it, but the tube basing caught my attention. I took a chance and paid him three dollars for it. Tom C. was at the meet with his CRT tester, so he later tested it for me. I think the crt is a 5AXP4. Does anyone know if there were any other crt's that were made this size? I tested the tube in an Admiral 20X1 chassis I just finished recapping. This test crt will make it easier for me to work on the old RCA's where the crt is installed from the front. I have about 5 more to recap yet.
Ed

Hello,
Last weekend at the WARCI , Milwaukee swap meet I saw this crt in the rear of a seller's van. It had no numbers on it, but the tube basing caught my attention. I took a chance and paid him three dollars for it. Tom C. was at the meet with his CRT tester, so he later tested it for me. I think the crt is a 5AXP4. Does anyone know if there were any other crt's that were this size made? I tested the tube in an Admiral 20X1 chassis I just finished recapping. This test crt will make it easier for me to work on the old RCA's where the crt is installed from the front. I have about 5 more to recap yet.
Ed

I seem to recall 8KP4 being a "test" tube in an article about bench testing chassis. I have a test CRT, no numbers, and I've never used it. It came with about a half dozen harnesses and an HV extender that was trashed.
I'll get some dimensions this weekend and see if my CRT matches up to anything I can find.

EDit - Not an 8KP4 for sure - 8KP4 is a rectangular CRT....

8YP4 is one of the other ones and the other is the 8XP4.

Some information about the "test tubes".

https://www.antiqueradio.org/8XP4PictureTube.htm

https://www.antiqueradio.org/5AXP4PictureTube.htm

http://www.radiomuseum.org/tubes/tube_8yp4.html

Thanks Brian and KVFLYER,
I wasn't sure if any other 5 inch round test crt's were sold.
I forgot Phil's website had info on test crts.
Ed

The full line, from Sylvania: