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#16
03-02-2005, 03:59 PM
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Interesting what you say about no reports of repairmen with cancer.....I've heard that some broadcast engineers who were exposed to transmitter radiation (AKA Microwaves) had LOTS of health problems as they were literally being cooked from the inside out.
There's story, which may just be urban legend, of an engineer who worked at the Empire State Building transmitter in the early/mid 50's who seemed to age 30 years over the course of a single year and died. His wife sued someone over his early death...don't know anymore of the details....does anyone? Then again, there are the Darwin Award winners such as the night watchman who was stationed out in some frozen tundra and noticed that when he passed in front of a microwave link antenna that he felt warmer.....so he pulls up a chair and starts sucking a bottle of booze inside out----he passes out and his crusty carcass is found the next morning! Please pass the BBQ sauce, YUM! Anthony 
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#17
03-02-2005, 04:02 PM
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I will try to remember to take the camera home tonightand see if I can get in to where the set with the lead shielded tube is...there has been recently more TV's acquired than I have been able to find really good spaces for so they have piled up in the garage. The set is a 25V" rectangular G.E.
So far as I know, have never seen any other brand of set with this tube. Consumer reports must have included tubes with leaded glass in their write up of lead shielded tubes...most color sets using tube HV rects used the regular old 3AT2 or 3A3C.
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#18
03-02-2005, 08:09 PM
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#20
03-02-2005, 09:24 PM
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Actually, I talked to an older TV guy who said he knew of no cancer cases w.r.t. color TV.
Realize, it's not just color sets that do it, though they got the attention. Typically, anything above 16kv absolute potential was considered to be good for it. From what I understand, even color sets are at the low low low end of the spectrum - low energy and it can't go far anyway. I'd be more worried about zapping yourself  BTW, I *think* NTE still sells those solid state HV rect plug ins, and at least that cuts 2 sources out of it... IIRC, the metal shield can around the tubes itself is beyond sufficient for shielding. I've seen dark 6BK4s and a few dark 3A3s. Never saw a 2AV2 or such, though. I don't think dark = wasted, but it's a good sign the tube's been around the block a few times... Hey, anyone remember all the fun 'fixes' that happened in the 70's and the fun failures of them?
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#21
03-02-2005, 11:12 PM
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I knew a TV repairman who had a heart attack and died after lifting one of the giant, real wood, consoles from back in the 1960s/1970s. Of course, he smoked and was very overweight. I wonder if this had anything to do with it? HM? I also have never heard of any issue with TV repairmen getting cancer or other illnesses from the radiation from TVs.
Remember B&W TVs do not have a metal shadow mask, the X-ray risk from these is much less if, it even exists, than from the color TV sets. I have about 3 types of tubes that are HV regulators for tube type color TVs. They all look like a 6BK4, but they have different pin-outs and are not interchangable.
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#22
03-03-2005, 06:14 AM
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Have a Conrac b/w monitor which uses a 6BK4....was from a TV station and included features like this that were absent in consumer b/w sets. There is no shielding at all around the 6BK4 so I figure the HV is low enough where x-rays aren't a concern.
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#23
03-03-2005, 06:29 AM
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Guys, is there any market for these tubes you mention? I have a lot of them, and would be delighted to make someone a package deal on them all.
__________________
deHavilland UltraVerve+Aries 845; L. Moore UltraFi Monaco Tannoy GRF-R, DMT15; '52 Jensen Imperials+JBL LE15B; JBL 2226+2441+Edgar, Yuichi horns
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#25
03-06-2005, 10:05 PM
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The Magnavox T931 chassis I have uses the 6BK4B -
don't know how long-lasting they are, but would be happy to get a spare or two. I remember the Xray scare when I was at Motorola - don't recall which tube it was (I worked on B&W design), but I do recall that the xrays were internally shielded by the electrodes if they were straight - but some tubes were manufactured with the electrodes crooked, and xrays could escape from the tube (at the bottom, I think). In the Magnavox t931 chassis, the tube is installed with the bottom toward the back of the set, and that side of the shield box is open - the 5 other sides are solid. (1967 model, 25AFP22 rectangular CRT, would be called 23V today). HV regulation was abandoned in later color sets when it was discovered that the sweep current could be made to track the high voltage variation with beam current- so on bright pictures, the HV drooped, which would have increased the size, but the sweep B+ also drooped and the size remained constant. Part of the internal factory design specs was the maximum percentage of size variation with brightness that was allowed. Regulated sets had no HV droop, but then the sweep current had to be maintained constant under varying beam current loads - probably easier in sets where the video b+ comes off the line instead of the flyback like later transistor sets.
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| Audiokarma |
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#26
03-06-2005, 10:40 PM
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I am presently working on a Sears 12" color hybrid set from 1971. This set was made in Japan. On it, the high voltage regulation is accomplished by regulating the screen grid supply to the horizontal output tube. 1/2 of an 8FQ7 is used. I had not seen a design like this before.
After replacing a defective 1 meg resistor, the circuit is working, but some blooming is occurring on bright pictures. The high voltage at minimum brightness is within the Sams listed specification. I plan to replace the 3AT2 high voltage rectifier to see if this reduces the blooming.
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#27
03-07-2005, 07:02 PM
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