10BP4 - bubbles in glass
 

I took a chance and picked up an untested CRT on eBay. It turned out to be a 10BP4 removed from an RCA 721TS. Too bad the set didn't come with the tube.
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At first, it tested very weak.
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After about two hours right in the middle.
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After using the "rejuvinate" function, it read a little better. I popped it into an Admiral 24A12. I need to adjust the ion trap and centering a bit, but otherwise it's working fine.
That means I have a good CRT for my GE 802 :)
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Something I noticed in both this 10BP4 and the old GE 10FP4 is a lot of bubbles in the face. So do some of my 7JP4s. The newer CRTs I have of those types don't have any bubbles. I wonder if these defects were common in early tubes ? They are somewhat visible if you sit cloes and know where to look. I suppose they're the equivalent of a dead LCD pixel today.
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I have some with bubbles, and also black inclusions. One has something like brush marks on an area of the phosphor. Kind of like they sanded the mold to touch it up and it transfered to the glass then.

I often wondered if if these were seconds that wouldn't have been installed in a new set.

John

The two 10" tubes I have right now (both GE brand) both have bubbles on the faceplate, but they are towards the outer edge of the screen.

Looking at the label on yours makes me wonder-did the tv shop pull this from a 721ts when making a crt change? It lists it's "defect" as being the original tube in the set, which tells me it was worn out, which it kind of tested as being. Maybe they hung onto this one to sell back to some other poor slob as a gently used crt.

One thing about metal CRTs, the faceplate is a precision piece of glass.

LOL - that could well be. I suppose it's a rebuild candidate too. After working with an electrostatic set lately, I'd forgotten how much of a pain it is to adjust a 10BP4s trap magnet, focus control and centering screws :drool:

I just had to spend an hour setting up the GE 802 in the owner's home. Gotta love those magnetic focus sets.

As far as repairmen hanging onto junker tubes, I have plenty of proof that it happened-I have an entire tube caddy of nothing but used tubes. There are copious notes written on each box about how each tube wouldn't work in the Anderson family's set, but maybe in certain other sets, etc. It has scads of 1B3s that have an ashen burn ring around their bases from being run to death. Quite an impressive collection of worthless tubes that were waiting to go into an unsuspecting customer's set for the full replacement price.

It was kind of an unwritten rule in Dad's shop to never throw away a 6GH8 or 5GH8 - they might work as a color oscillator, but not in horizontal circuits, or vice-versa. I fixed a metal cabinet set for a friend across the river in Portsmouth by merely swapping 5GH8's from one socket to another. His wife swore I did something else, but my buddy was right there to see me move them - and swapping them back recreated the problem (an AGC like buzz from leakage from the vertical oscillator). So what doesn't work in one set may work fine in another - the inter-electrode capacitance of tubes varies widely and can cause such problems. Similar effects carried over to IC's - the early Resistor-Transistor-Logic chips might work in one circuit but not another. I was left scratching my head when a calibration tech fixed a Doppler Radar Test bench by merely swapping two RTL chips. :scratch2:

Cheers,

My DuMont 20BP4 has some nice bubbles in the front glass. Seems this must have been pretty common.

Consider the bubbles part of that set's character, like the fleck of tobacco stuck between the screen cover and CRT face on my Predicta. No way am I horsing that cover off just to remove it, so the fleck is here to stay. These little blems are forgotten when you're actually watching a program. When you kissed that cheerleader in high school, you forgot all about the tiny pimple on her forehead.

Phil