21CBP4A in place of 21WP4X??

[H2s04]

I picked up a rebuilt 21CBP4A for $5 at a "junk shop" in NH today. I'm restoring an Admiral 19G1 that came with a 21WP4X, the base of which is broken. It looks identical, and wondered if it's a suitable replacement.

One other question; the sticker on the bell of the tube that says in bold, bright letters saying "DO NO USE AN ION TRAP WITH THIS TUBE. IF REPLACING A TUBE THAT USED AN ION TRAP, DO NOT USE AN ION TRAP" Why on earth is this?

[Eric H]

Hi Jeff, according to my sub book it won't work though it doesn't say why, it could operate at different voltages or maybe has a different method of focusing. Perhaps someone has a more detailed tube book that will give details?

The 21CBP4A is probably an aluminized tube, they don't need and in fact won't work with an Ion trap.

The gun assembly is mounted at an angle on tubes with Ion traps, the trap is used to straighten the electron beam out so it hits the screen while allowing the heavier ions to hit the neck of the tube where they will do no harm.

The Aluminized tube has the gun mounted straight, electrons and ions both hit the screen but the Aluminum coating prevents any damage.

Eric

[H2s04]

Thanks eric, thats somewhat depressing though. Anyone else know? I'd really like to use this tube!

[bgadow]

The one book I checked says the 21WP4 has no subs. (aside from suffixes, A, B,etc) The GE Essential Characteristics book lists differences as being: CBP is electrostatic focus vs. magnetic on the WP4, & the WP4 is listed as having "dimensions different from normal". There are some other differences but those are the major ones I see. I think the CBP was fairly popular? I have a pair of Motorola's that use it, from 59/60. One has a weak crt but I have a NOS rebuilt in the attic waiting.

The 21WP4 is slightly smaller than other 21" types. The screen diagonal measurement is 20" instead of 21". No clue why they didn't call it a 20WP4 - must have been a marketing decision. The tube was first introduced and manufactured by National Video Corp. in Chicago, and was extensively used by Admiral, who advertised the models using it as "21 inch".