Steven Swift wrote:
According to my DuMont handbook of CRTs, a yellow filter can be
used with a P7 phosphor CRT to allow viewing of the long decay
part without being "blinded" by the bright blue trace. I've searched
Ebay, Sphere Research and other sites looking for these.

Anyone have one good for a 3" round CRT or know of a good substitute
material (perhaps from a hobby store)?

Theatrical lighting gels should work fine. Try a theatre supply store.
Ask for a "******* amber" gell, or a "#13 straw." Gels usually come in
both wide rolls and small squares that should be fine for a small CRT.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."