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  #46  
Old 11-05-2007, 09:34 PM
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Just for the record, what kind of temps are we talking about and what type of oven is this in? I sure hope there aren't people trying this in their typical Tappan oven....

By the way I have found this thread very interesting and have learned much from it. Thank you.
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  #47  
Old 11-06-2007, 07:36 AM
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CRT Rebuilding equipment

With all of this interest in CRT rebuilding, it begs the question, why doesn't anyone want to experiment?

Twice over the course of the last 15 years, I've been offered CRT rebuilding stations from defunct shops, and I've have never found any one willing to buy and/or pickup the equipment. One offer to me was for a free set-up (Come and get it!), and the other was for about $1,000 or $2,000.

I also remember one or more set-ups offered on ebay in the last 5 or 6 years.

I always wished I could make the room, and the time, but if I had taken any of these, they'd still be kicking them around in the back of my garage!
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  #48  
Old 11-06-2007, 10:36 PM
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Experiment on whose CRTs? How many guinea pig tubes would it take to gain "experience" ? And how valuable would that experience be if you finally succeeded in rebuilding one usable tube after dozens of rejects--is that when you'd hang out your shingle? Scary thought.
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  #49  
Old 11-07-2007, 11:56 AM
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Doesn't the rebuilding process require some new parts? Where would a person find them? Old P1 or P7 CRTs (non P4) are a dime-a-dozen still and would be good for practice. I suppose a person might take the gun & neck from a NOS 5FP7 and put it on a no-emission 7DP4 and make it worth his while. Could a person mount a set of color guns from a modern-ish Zenith rectangular CRT onto an "aired" 15GP22? Beats me.

I'd give it a shot if anybody wants to offer his "Come n get it" special (and you're not on the far side of the moon). I would think ten ten-dollar 'scope tubes would be a worthwhile hundred-dollar learning experience, to set up shop rebuilding those 500-dollar RCA 621TS tubes.
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  #50  
Old 11-27-2007, 04:50 PM
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I think the only way that this could be successfully done is for someone to become an apprentice to Scotty at Hawkeye for a few months to learn the art.
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  #51  
Old 11-27-2007, 07:43 PM
julianburke julianburke is offline
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It's built the same way as a glass tube. We actually had less trouble with the metal tubes than the glass ones.
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  #52  
Old 12-12-2007, 10:41 AM
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Quote:
Originally Posted by yagosaga View Post

One can do with such a bunch of rays only a little, especially if one wants to get a sharp limited single spot on the screen. If one fills in the existing glass tube with a noble gas, for example, helium or argon, one can achieve a sharp focussed spot of the rays if one surrounds the filament with a metal cylinder which must be connected with a negative voltage.

The problem in these days was the focus of the cathode beam. They did not have proper electronic focus lenses. With the adjustment of the negative voltage for the metal cylinder, the beam was focussed on the screen.

In the later tv sets of the end of the 1930s (see for example the E1), they used electromagnetic coils for focussing the beam.

- Eckhard
Eckhard is correct on this. Most crt's in the 1920's and early 30's were of the gassy type. The gas was actually used to focus the electron beam as there was no good way to focus it in a hard vacuum type tube at the time. While this worked fine for oscilloscopes and such test equipment, gassy tubes are not very suitable for use in television. A gassy tube can only be focused over a narrow band of beam currents. Since the beam current needs to be modulated for television, this resulted in poor focus.

Zworykin while working at Westinghouse in 1929 developed and patented the first hard vacuum crt with an electronic lens. This is what he called the "kinescope" and is the basis for all modern crt's. It is said that most experts of the time scoffed that this was impossible, and RCA did not publicly show the kinescope until May of 1932, and then only to RCA licensees.

Darryl
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  #53  
Old 12-12-2007, 03:25 PM
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Quote:
Originally Posted by tubesrule View Post
While this worked fine for oscilloscopes and such test equipment, gassy tubes are not very suitable for use in television. A gassy tube can only be focused over a narrow band of beam currents. Since the beam current needs to be modulated for television, this resulted in poor focus.
Hi Darryl, these early German gassy picture tubes were used up to 1936. From 1937 and later the CRTs were high vacuum tubes.

In a gassy tube the negative voltage at the metal cylinder was adjusted for a focussed beam with maximum brightness. When the beam current was lower or low, the focus became poor, and as a result, the point on the screen became darker. In this way, one effect of the gassy tube was an improvement of contrast, but a loss of gradation.

The high vacuum tubes generated a more natural b/w picture with an improvement in gray tones and gradation.

- Eckhard
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