EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: calexanian on February 13, 2017, 02:42:12 am
-
https://www.youtube.com/watch?v=G0Dci5RPe94 (https://www.youtube.com/watch?v=G0Dci5RPe94)
A video showing the manufacture of ceramic CRT's from Tek in the 60's
-
Fascinating video. It never ceases to amaze me how much goes into making something that is so taken for granted.
-Pat
-
You wouldn't have taken it for granted if you had to buy one new back in 1965. :-DD
Tim
-
I'm more used to seeing CRTs with just one "second anode", painted in aquadag over the inside of the glass bell. It looks like in those ceramic tubes, Tektronix used multiple post-deflection electrodes. What were they for and where is that theory documented? Thanks.
-
Great video and love the visual and narrative style. VintageTEK Museum has posted some good stuff that I've watched the last few days.
-
I'm more used to seeing CRTs with just one "second anode", painted in aquadag over the inside of the glass bell. It looks like in those ceramic tubes, Tektronix used multiple post-deflection electrodes. What were they for and where is that theory documented? Thanks.
It's "travelling-wave" construction. It's an array of deflection plates mounted and spaced that the beam, in passing between the successive plates, receives an additional amount of deflection. This effectively enables the construction of high bandwidth CRT's. Similar in function to how distributed amplifiers work.
Edit...here's some info....
http://ggnindia.dronacharya.info/EEEDept/Downloads/QuestionBank/Vsem/EMI/section-A/Lecture-7.pdf (http://ggnindia.dronacharya.info/EEEDept/Downloads/QuestionBank/Vsem/EMI/section-A/Lecture-7.pdf)
-
Here are some pictures of such a tube: https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/
Observation: it seems that reasonable professional scopes still cost two year's salary.
-
I've added collecting these in my recycling process , because I recognized that they were coated inside with gold , silver .
Now have to figure out how to separate the gold etc. from the ceramics ?
Not planning on getting rich , just does not make sense to through away , same with lot of other goodies .
-
Such thread shouldn't go without that excellent paper from Tek: http://www.davmar.org/TE/TekConcepts/062-0852-01_CRTs_Jul69.pdf (http://www.davmar.org/TE/TekConcepts/062-0852-01_CRTs_Jul69.pdf) via http://www.davmar.org/concepts.html (http://www.davmar.org/concepts.html)
-
I'm more used to seeing CRTs with just one "second anode", painted in aquadag over the inside of the glass bell. It looks like in those ceramic tubes, Tektronix used multiple post-deflection electrodes. What were they for and where is that theory documented? Thanks.
It's "travelling-wave" construction. It's an array of deflection plates mounted and spaced that the beam, in passing between the successive plates, receives an additional amount of deflection. This effectively enables the construction of high bandwidth CRT's. Similar in function to how distributed amplifiers work.
That's not what he's talking about, though that is the other important major feature in the design of these tubes!
The multiple anodes shape the accelerating voltage, changing the scale of the image (potentially distorting it, too, so this must be done carefully), optimizing the deflection sensitivity and image intensity.
The older tubes, that use a painted-on spiral, achieve a gradient field. The spiral of course is a resistor, so the 2nd anode always dissipates some power, even at zero beam current.
Some other CRT designs used multiple 2nd anode voltages, for improving secondary emission (in storage tubes, cameras), or I forget why but Trinitrons used a thing like that too, etc.
Tim
-
I've added collecting these in my recycling process , because I recognized that they were coated inside with gold , silver .
Now have to figure out how to separate the gold etc. from the ceramics ?
Not planning on getting rich , just does not make sense to through away , same with lot of other goodies .
If they're functional, in my opinion it would make more sense to sell them to people who might need replacements or want to have a spare on hand. I rather doubt the amount of precious metals in one would be worth the effort involved in attempting to recover it.
-Pat
-
I'm more used to seeing CRTs with just one "second anode", painted in aquadag over the inside of the glass bell. It looks like in those ceramic tubes, Tektronix used multiple post-deflection electrodes. What were they for and where is that theory documented? Thanks.
It's "travelling-wave" construction. It's an array of deflection plates mounted and spaced that the beam, in passing between the successive plates, receives an additional amount of deflection. This effectively enables the construction of high bandwidth CRT's. Similar in function to how distributed amplifiers work.
Edit...here's some info....
http://ggnindia.dronacharya.info/EEEDept/Downloads/QuestionBank/Vsem/EMI/section-A/Lecture-7.pdf (http://ggnindia.dronacharya.info/EEEDept/Downloads/QuestionBank/Vsem/EMI/section-A/Lecture-7.pdf)
An example of how this is driven and terminated in the 7904 can be seen on page 230 of http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf (http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf)
Though it was somewhat more instructive to see the side of the tube, where that board sits directly at the connections, and somewhat further forward is the termination resistor network.
-
Am I the only one that feels that modern documentaries and technical shortfilms aren't even nearly as good as the old ones from 60's to 80's .. or am I just getting old :scared:.
-
Here are some pictures of such a tube: https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/ (https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/)
Observation: it seems that reasonable professional scopes still cost two year's salary.
Related, here's a close-up of my Tek 475's distributed vertical deflection structure:
(https://www.seventransistorlabs.com/Images/Tek475_5.jpg)
Curiously, the pitch increases along the structure. Not quite sure what the equivalent circuit is -- it seems to be a spiral around, which wouldn't make sense. Perhaps it's segmented, maybe folding back on itself in the process? I think there were coils too (out of view), which would be in line with the earlier distributed plate design documented in the above whitepaper.
Tim
-
Am I the only one that feels that modern documentaries and technical shortfilms aren't even nearly as good as the old ones from 60's to 80's .. or am I just getting old :scared:.
One issue is that back then it was difficult and expensive to make and distribute videos. Consequently much more thought was put into what needed to be taught, and how to get it over.
Now it is simple and cheap, everybody and their dog does it :(
-
24 inches of tube to make a 4" screen. My lap top would be eight feet long using one of those screens. I should make one.
-
I've added collecting these in my recycling process , because I recognized that they were coated inside with gold , silver .
Now have to figure out how to separate the gold etc. from the ceramics ?
Not planning on getting rich , just does not make sense to through away , same with lot of other goodies .
Its an alloy but you may be able to dissolve it via one of the many gold recovery methods. Lots of videos on that out there.
-
The tubes are much more valuable in their intact state than the value of the materials they contain, assuming they are still usable. Nobody is making CRTs anymore and there are a lot of instruments using them still in service.
-
24 inches of tube to make a 4" screen. My lap top would be eight feet long using one of those screens. I should make one.
Yeah, electrostatic deflection doesn't seem to bend an electron stream quite as aggressively as a magnetic deflection yoke - no direct writing 110 degree scope CRTs out there that I know of. On the other hand, good luck getting 350MHz bandwidth out of a magnetic yoke!
-Pat
-
This earlier one (also from VintageTEK Museum channel) is good ->
https://www.youtube.com/watch?v=q5dhfhMItQc (https://www.youtube.com/watch?v=q5dhfhMItQc)
-
Watching those videos it is no wonder scopes were so expensive. All those manual hand operations, and such low production rates. A very labor-intensive task, building up just the CRT. Not to mention assembling the chassis and those ceramic tab component mounts to hold all the discrete components. Wow.
-
I saw both of these in Junior High.
They were Great.
:-+ :-+
-
The multiple anodes shape the accelerating voltage, changing the scale of the image (potentially distorting it, too, so this must be done carefully), optimizing the deflection sensitivity and image intensity.
From my own experiments, I know that the PDA on these CRTs combined with the scan expansion mesh roughly doubles the deflection sensitivity.
The Tektronix Circuit Concepts book Lukas linked discusses this in detail.
Am I the only one that feels that modern documentaries and technical shortfilms aren't even nearly as good as the old ones from 60's to 80's .. or am I just getting old :scared:.
One issue is that back then it was difficult and expensive to make and distribute videos. Consequently much more thought was put into what needed to be taught, and how to get it over.
I think there is more to it than that. Companies dropped detailed service documentation as patent lawsuits became a real threat. At this point it would just be dumb to explain anything publicly and invite an intellectual property lawsuit whether the lawsuit had merit or not.
Another reason not to publish such information is that the US patent office has a very limited view of what constitutes "prior art" when a patent is being examined so trolls go through various public documents, patent what they find, and then later sue. The courts operate under the assumption that the patent office was strict in examining the patent even though this is not the case so they apply it broadly.
-
24 inches of tube to make a 4" screen. My lap top would be eight feet long using one of those screens. I should make one.
Yeah, electrostatic deflection doesn't seem to bend an electron stream quite as aggressively as a magnetic deflection yoke - no direct writing 110 degree scope CRTs out there that I know of. On the other hand, good luck getting 350MHz bandwidth out of a magnetic yoke!
Exactly, try to apply even 100MHz of deflection magnetically. Some oscilloscope CRTs did use magnetic horizontal deflection but even that is difficult at higher sweep speeds where bandwidths between 1 and 3 MHz are typical.
The problem has to do with the electronics driving the vertical deflection plates. At high frequencies, it is very difficult to supply the voltages necessary simply because there is a trade off between transistor speed and breakdown voltage. So ignoring other limitations which are solved by using distributed deflection, higher deflection sensitivity is equally necessary for short tubes which have large screens *and* high bandwidth vertical deflection. The small area of oscilloscope CRTs reflects the requirement for high bandwidth despite their relatively long tube length. The long length is needed so that the deflection sensitivity is high enough that the lower deflection voltage from a faster vertical amplifiers is acceptable.
During the Cold War, the Soviets had 13 GHz scan converter CRTs for their nuclear weapons tests while we were limited to 5 GHz despite all of the tricks we used because of the US Government specification required the test instrumentation to fit in a 19" rack which limited us to 5 GHz. The Soviet's solution was to make their CRT scan converters 6 meters long.