I know that no matter if the set be black and white or color; safety glass or no that television repair training used address x ray radiation. It used to be taught that a tech should never reach over a working set having the face of the c.r.t. close to his chest. This was considered dangerous, so there must be a significant amount of radiation coming out of most all c.r.t. sets. Now the mention of the eventual use of lead may change that some; I don't know, but I always think about that when working on any set.

Also, I know that the whole radiation scare for the viewer more or less came along with color TV for whatever reason(s). As a kid I remember moms always making us back up from the color TV which had some strange attraction that made us want to get as close as possible. They talked of harmful radiation and danger to our eyes.

The early 6BK4 HV regulator tubes (before they were made with lead glass) were known x-ray emitters.

jr

The caution for service techs was because X-radiation damage is cumulative. You would not be harmed significantly by one exposure, but day in and day out would not be so good. Same reason x-ray technicians leave the area to take the picture.

The regulator tube problem was not leaded vs. unleaded glass, but tubes that were constructed crookedly so that the source of x-rays at the anode was not blocked by the metal structure at the bottom of the tube. If a defective regulator was mounted vertically and had no shielding underneath, a kid sitting up close with legs under the set would have his legs in the path of the stray x-rays.

Interesting! But wouldn't the leaded glass envelope for the 6BK4 reduce the X-ray emission regardless? or was the stem/header at the base not leaded glass?
Our family cat got better after the 6BK4 was replaced with a leaded one. :)

jr

As to the front face, bonded or un-bonded there is the protection of x-ray shielding if followed in early interchangeability instructions as well as implosion protection. Even if the front glass is not leaded it would provide protection from "soft" x-rays being emitted as there is that "additional layer". Granted, leaded glass is better I know. The manufacturers' had to ensure precautions from a liability/safety standpoint as well as maintaining interchangeability standards for tube replacement back in the day.

As many of us may have noticed, a curved face for a 21FBP is about twice as thick as a 21FJP. The bonding does make up for some difference though.

I do believe we are plenty safe after doing cataract surgery although I will still maintain my distance!

I know of a retired CRT rebuilder and when he's back in town I'll run have to run this past him.

...

A little info here on this old thread:
http://www.videokarma.org/showthread.php?t=250046
jr

I've got a tube soaking now - Channel master rebuild 21FBP22. Yes. It's got a faceplate - weird, huh?

Anyway, after about 2 (or was it three?) weeks, it's very obviously starting to come apart - the material at the edge has debonded entirely from the glass. Interestingly, it's also become quite brittle (the ambient water temp - mid 50's - might be a factor too?). There's a few inches in the center that are obviously bonded, and I'm pretty sure that after a few more weeks, it'll let go.

It seems the plasticizers get leeched out by the water, and it just lets go from the glass. It's certainly a slow process (maybe warmer water helps?), but it seems to be making progress.

I'm getting really curious as to WHAT this stuff is...

I prefer to do my tube soaks in the summer months!

It's important to have the water at the same temp as the tube to minamize any thermo stress..

Well, it's been at a stable temp for 3 weeks now. At the rate this winter's gone, I don't think it'll ever get hot for the summer :(

I've seen 3DS3 tubes with a lead jacket. In what application do you think they were used?

My retired rebuilder guy used to work for Video Display Corp in Dallas. According to him, the bonded face glass was there for implosion protection more than anything and were not leaded.

video display rebuilt two tube for my and they still strong. I think the guy's name used to be Phill. They were located at Profit Drive. I missed their services. also Louis Stangle from united tuner repair.

Ok - the tube I'm soaking is coming along nicely. The faceplate (but not the tube!) cracked (mechanical stresses from the clothespins being a bit enthusiastically applied), and I pulled most of the pieces off. The remainder is soaking, but water seems to make slow but sure inroads into it.

What the heck is this stuff? After soaking, at ambient temperature (55-60 degrees, it's very brittle and not exactly clear. I'm guessing water leeched out the plasticizers from it. It's about 1/16th inch thick. Along the sheets of stuff I've broken off, they're pockmarked with areas where it decayed in advance.

What causes the decay? Possible hint:This tube came from a water-damaged box. Moisture ingress? But that doesn't explain the decay towards the center. Maybe it's an unstable compound - but I've got two RCA tubes that show virtually no sign of delamination (I think this tube's an RCA, too).

Everyone calls it PVA - have we gotten a confirmation that it actually *is* PVA?

Oh yeah, it burns really sooty and is pretty self sustaining once it gets going. Heat softens it up a lot. I tried acetone - no effect.

Is this stuff perhaps really a silicone of some sort? RTV, maybe?

Used in early '70s GE color sets due to X-ray hysteria. Jacket is lead oxide.