Eye Tubes: A Friendly Word of Caution

[WA4WAX]

This is aimed at newcomers.

Eye tubes are cool: 1629, 6E5, etc.

One work of caution:  Keep them out of direct sunlight!  For that matter, keep them away from any strong, direct light.  Many times I have seen an eye tube radio or test gadget out on a swap meet table, uncovered, with the blazing sun impinging!

Sunlight will bleach and ruin the phospor; do NOT do it!  If you have strong, direct ligght in your shop or shack, keep your eye tubes covered!  BTW, CRT phosphors probably do not like sunlight either.

On a related note, keep both phototubes and photomultipliers (PMT's) OUT of strong light!

If you have a PMT, and it gets zapped, here is what you do:

Put it in a small box with some dissicant.  Go to a university, and find some bio guy with a -80C freezer.  Put PMT in freezer for a few days.  Let it warm up slowly before removing it.  Repaet process a time or two if the dark current does not come back down to specs.

This often works.  Often, not always.

Matt :-)

[W3NE]

I never knew that. I love those glowing eye tubes, so thanks!
Bob - NE

[Opcom]

I wonder if CRT phosphors can be bleached/ruined the same?

A note about projection TV CRTs with integral lenses. Don't point them out the window. If the sun's rays come straight in then they will be focused on the phosphor. It usually won't harm it because of the liquid coolant, but it will melt the plastic lens in the area near the tube face.

[w3jn]

Bill Turner, a former regular contributor to the Antique Radio Forum, disproved this by putting an eye tube outside for several months.  No change in brightness.

https://web.archive.org/web/20060713012436/http://www.dialcover.com/eyetube.html

[Todd, KA1KAQ]

When you think about it from a common sense perspective, this would've been a disaster for the big radio manufacturers back in the 30s were it true. With millions of people buying sets for the home back then, you just know plenty were set up where they were either in direct sunlight (easily seen today on sets with faded finishes) or in a spot where the sun struck them for enough time each day to 'destroy' the eye tube. At the very least, this would've caused manufacturers to post a warning inside the owner's manual about placement. Yet no manual I've ever read, pre-war especially, has mentioned it.

Makes you wonder if maybe this somehow came about as some sort of reverse-burn-in theory based on damage done to CRTs by a static image.

It does remind me that I need to find a 6T5, however.... 

[KA0HCP]

CRT phosphors vary greatly in sensitivity to bleach out effect.  It is not possible to make blanket statements about them.   There are a couple of classification systems for CRT phosphors that describe their characteristics that include the other main property; persistence.

[w4bfs]

Bill Turner, a former regular contributor to the Antique Radio Forum, disproved this by putting an eye tube outside for several months.  No change in brightness.

https://web.archive.org/web/20060713012436/http://www.dialcover.com/eyetube.html

you reckon he kept an eye on it 

[w8khk]

My favorite was the 6AF6 dual tuning eye, that did not include the triode amplifier.  It was used as a stereo record level indicator in the old RCA cartridge recorder.

Also the 6AL7, with two rectangular displays, used for tuning and signal level in a home-brew 40s FM tuner.  Very interesting tube!

[Opcom]

all very nice