View Full Version : 21EP4B sub for 21YP4


ed857
08-16-2016, 02:50 PM
Hi all

I have a Philco with a weak 21YP4 CRT. I also have a NOS 21EP4B rebuild.

Will the 21EP4B sub for the 21YP4? The bulbs sure look the same.

Thanks,
Ed :)

dieseljeep
08-16-2016, 03:01 PM
Hi all

I have a Philco with a weak 21YP4 CRT. I also have a NOS 21EP4B rebuild.

Will the 21EP4B sub for the 21YP4? The bulbs sure look the same.

Thanks,
Ed :)

The 21EP4 CRT is a magnetically focused, cylindrically faced CRT. The 21YP4 is an electrostaticly focused, spherically faced CRT. To use the 21E as a sub, a magnetic focalizer, would have to be fitted, but the CRT face would not match the mask opening. :sigh:

ed857
08-16-2016, 03:11 PM
Well.............Rats:tears:

Thanks for the reply:thmbsp:

Ed

Electronic M
08-16-2016, 03:58 PM
I've got a spare PM focus unit off of a large neck Philco CRT, and I've put tubes with different face curves in other tubes mounts successfully. It could work...The edges of the mask won't fit the screen in as visually pleasing a manner as the original though...

If the original ain't watchable with a brightener, may as well try the swap....

Robert Grant
09-03-2016, 11:25 PM
You're not thinking of the 21AEP4, are you? (That would be a sub for a 21Y, and saves you the bother of aligning the ion trap).