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 Post subject: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 4:13 pm 
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I have read that excessive x-ray exposure can cause some types of glass to darken or brown. This is from a misc collection of tubes and is a 6BK4C which is designed for HV (up to 27000 volts) shunt regulator in some TV sets. Looks like it has had it's share of x-rays, defiantly not NOS. Just thought this was interresting.


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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 5:04 pm 
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I think it is more likely to be nicotine stain than x-rays. When I worked in a TV service shop, I always dreaded working on TVs that were in taverns. The HV items really attract fine particles.

When I worked at Westinghouse, I did an experiment to see if we could improve the switching speed (trr) of already assembled diodes using electron irradiation at a reactor near San Diego. The black epoxy turned chocolate brown and the diodes had an insignificant improvement in trr. I think radiation works on plastic, but not on glass.

Rich


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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 5:12 pm 
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Rich, W3HWJ wrote:
I think it is more likely to be nicotine stain than x-rays. When I worked in a TV service shop, I always dreaded working on TVs that were in taverns. The HV items really attract fine particles.
Rich

No, based on your comment I tried to wash off any outside coating and nothing came off with soap/water, so it is the glass turned brown. Somewhere I read that TV shunt regulators were an x-ray problem until they did away with shunt regulators on later TV's.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 5:14 pm 
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It's definitely not nicotine, it's actually inside the glass itself, as in the glass gets darkened from the X-rays created inside. They start out clear except for the getter flash area, and gradually get darker and darker with extended operation time.

I've changed literally hundreds of them which were so darkened the glass was nearly black. That comes from long hours and years of operation. Some of them would actually still regulate when they were that dark, but eventually got weak enough that the HV would be too high.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 5:19 pm 
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I found this:
Quote:
The most popular method of regulation uses a simple shunt regulator across the 25-kV supply. This introduces another source of X-radiation. Electrons striking the plate of the regulator tube at 25 kV must give up their energy at the plate in the form of heat and X-radiation.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Thu 08, 2020 10:54 pm 
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This happens with other types of glass. I had to investigate why the fiber optic glass darkened on the space station. They even discussed sending me up there. It apparently came from cosmic rays. The darkening leveled off and they could compensate for the loss of transmissibility. They were able to up the transmission power of the signal transmitters so I didn’t go.


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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Fri 09, 2020 12:34 am 
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I remember getting a discarded x-ray tube from a local hospital when I was in high school. Certain parts of the glass envelope were more yellow-brown than others, but I didn't understand the effect that x-rays had on the glass itself at the time. The chemical composition of the glass would certainly make a difference in its response to irradiation. No doubt mass-produced consumer items like 6BK4s were more susceptible to darkening than lab-grade x-ray tubes.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Sat 10, 2020 1:30 am 
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I'm never too old to learn.

Thanks.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Sat 10, 2020 2:32 pm 
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AFAIK it's the lead content in the glass that x-rays cause to darken.

Early versions of 6BK4 & maybe 6BK4A didn't darken nearly at rate of the later B & C versions. As x-ray regulations tightened, lead content in glass increased. I've seen examples that were totally blackened.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Sat 10, 2020 3:19 pm 
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I don't have a 6BK4, but found this.

Only opened box because it was heavier than most other tubes.


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6LJ6 002.JPG
6LJ6 002.JPG [ 571.26 KiB | Viewed 757 times ]

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Sat 10, 2020 11:34 pm 
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You just reminded me...

It might not be X-Rays (although the theory and evidence are attractive). It might be lead in the glass. We saw this happen in Oz when Philips had a problem with envelope cracking on hot tubes (e.g. 6CM5, 6AL3) after mains gas changed from methane to propane (i.e. "Natural Gas). They added lead to the glass and, after a few weeks of use, a very similar brown stain would happen. This happened right at the end of tube production in early 70's.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Mon 12, 2020 4:17 am 
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Dennis Banker wrote:
This happens with other types of glass.
In historic neighborhoods around here, some sidewalks have pavement lights ("sidewalk prisms") to convey daylight into spaces under sidewalks. Many of those glasses have turned purple from UV exposure during the century (more or less) since they were installed.

Ironically, according to this article, the purpling occurs in compounds such as manganese dioxide that were originally added to make the glass CLEAR:

https://en.wikipedia.org/wiki/Pavement_light

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Mon 12, 2020 1:25 pm 
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If memory serves (occasionally) there was a recall and replace alert due to misaligned elements in the 6BK4 tubes producing X rays at levels higher than what was considered safe at the time. Seems possibly just RCA but it was 45 years ago ... memories can only store so much. Possibly this is one of those tubes that did not get replaced?

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Tue 13, 2020 5:02 am 
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I found a 23Z9 tube that looks a little brown...
Attachment:
IMG_20201012_215741_0.jpg
IMG_20201012_215741_0.jpg [ 822.2 KiB | Viewed 635 times ]

Has that smokey glaze to it...

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Tue 13, 2020 12:04 pm 
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I think I have mentioned this story on this site before but the last tube picture reminded me...

Back in the 60s, a tech pulled a chassis from a 10 year old TV in a pub at Balmain (Sydney suburb).
It was soaked in a toxic mix of nicotine, dust and gunge - there used to be two coal-fired power stations nearby and everyone smoked in those days.
And it STUNK to high heaven!
The head workshop tech, a heavy smoker, took one look, ran outside and threw up. He never smoked again!
The TV was condemned as a health hazard.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Tue 13, 2020 1:54 pm 
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Back in the ‘70s, my dad called me and said his TV caught fire. I went over to his house and looked at his set. It was an old 60s set. When I took the back off there was tar and around the hv section. The heat, electrostatic attraction and cigarette smoke made a stinky burned mess. I was able to lean it off and the fly back was not damaged. We always talked about the dangers of smoking but it never sank in. As an example, I removed a picture and showed him the clean wall behind it. The rest of the wall was greyish brown from smoke.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Tue 13, 2020 2:04 pm 
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Back in the old VCR days, I had the misfortune to maintain a pile of 3/4" videotape decks at a disco club. They were horrible .... you'd want to hose them down before touching them. Cigarette smoke and dust caked to everything it could stick to. Pinch rollers and belts lasted 3 months at most.

Made a ton of $$ but couldn't stay in that place longer than just 'scoop and run' with the misbehaving deck.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Wed 14, 2020 12:05 pm 
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Quote:
Back in the old VCR days, I had the misfortune to maintain a...
...fleet of pizza chain VHSs. Gnarly, dude. From what the outside guys who retrieved them told me, last place in the world I would ever eat.

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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Mon 26, 2020 4:11 am 
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irob2345 wrote:
I think I have mentioned this story on this site before but the last tube picture reminded me...

Back in the 60s, a tech pulled a chassis from a 10 year old TV in a pub at Balmain (Sydney suburb).
It was soaked in a toxic mix of nicotine, dust and gunge - there used to be two coal-fired power stations nearby and everyone smoked in those days.
And it STUNK to high heaven!
The head workshop tech, a heavy smoker, took one look, ran outside and threw up. He never smoked again!
The TV was condemned as a health hazard.


I repaired computers at car dealerships in the 70s and early 80's. At that time, most people in a dealership were chain smokers. I had to repair computers where the keys on the keyboard were impossible to read and the LED display dim from the smoke "chimney effect". I can still smell it, and I don't smoke anymore. We had optical feedback disks for printer carriage motors fail from cigarette smoke.

Hard to believe that those conditions were considered "normal" at one time.


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 Post subject: Re: How brown am I ? 6BK4C
PostPosted: Oct Mon 26, 2020 8:20 am 
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Car vinyl headlining that had changed color from pastel green to brown in my 1958 FC Holden (think '57 Chevy, 2/3 the size) also comes to mind. No detergent or scrubbing would shift it.

Attachment:
FC.jpg
FC.jpg [ 58.6 KiB | Viewed 366 times ]


My 2nd car, 1st one was forgettable!

By the way, this car was an ancestor of the Pontiac G8.

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