The beam current return path is back through the second anode. On aluminized tubes, the aluminum layer is connected to the second anode coating. On older non-aluminized tubes, the screen and phosphor itself builds up a considerable static charge, which slowly leaks across the glass (or through whatever contaminants are on the surface) back to the coated portion of the bulb. The static charge buildup on the phosphor can cause a phenomenon called "image sticking", where the image persistence starts becoming longer, and blurs details. This acts as a severe limitation of the accelerating potential, and consequently image brightness. Aluminizing the tubes was a great advance with 3 major improvements. Prevents phosphor damage from ion bombardment, reflecting light emitted from the backside of the phosphor screen in a forward direction (major brightness increase), and eliminates image sticking by providing an easy return path for the beam current. This allows the use of higher accelerating voltages, and even better image brightness.
I'd like to add something. Others and I have added a few answers here and there, so we can say the return path for the electrons is clear. Now, there is an interesting spin to this. There is a special case of CRTs, in which you indeed are interested in the electrons remaining as buildup charge. You see, the electron looses its kinetic energy when it hits the screen (be it into phosphor atoms, into lacquer coating atoms, or even glass). It obviously doesn't disappear. So the anode will start accelerating those electrons again, this time to the sides, in a motion parallel to the screen. Now, as the electron had no motion to start with, it will take time to accelerate, meaning the glass area will retain that static charge buildup for some time before it gets into the anode again. And "If it takes time... it's MEMORY". Regular oscilloscope CRTs were used as Williams-Kilburn memory tubes in early first generation computers. You simply needed a conducting faceplate at the outer face of the screen to sense that charge buildup, instead of your finger. And that provided a better return path (capacitive) than the HV anode. The charge would go away in a fraction of a second, but you could scan, read, write again, before it would vanish. But the anode potential was still there, complicating things because as electrons moved sideways they would eventually spill from a charged 1 area into an uncharged 0 area causing memory retention problems. As the 1950s progressed, specialized tubes were made like RADECHONS and other storage tubes, with the sensing faceplate inside the glass envelope, and usually with a wire mesh that isolated the buildup charge from the anode eliminating the spill problem, seriously raising the retention. And with an entire decade of research and funding, with things finally ready for a reasonably good computer memory, An Wang developed tiny magnetic cores, giving way cheaper, lifetime retention, binary memory with a rather simple binary addressing system... the storage tubes evaporated in the blink of an eye. Almost... because storage CRTs were able to retain ANALOG charge levels... not only binary. So they remained in a plethora of niche applications. The soviets used them in their radars up to the 80s! They were used as a memory to take a baseline and spot the difference (moving target) between two consecutive radar scans. Also scan converters of the 60s used these weird CRT contraptions, with one electron beam to one side, doing the writing and another to the other side of the screen doing the reading. The latest modern storage tube I am aware of, is a weird Tektronics storage/digitizing CRT (without a visible screen) which was used in some GHz oscilloscope I don't quite remember, I think in the 1980s. The scope had a regular CRT for its screen, and this weird thing inside to do the hard work. Physics is beautiful, and in those days you had these particle accelerators right there in front of your eyes, which you could play with in your garage. Every fluorescent tube in a ceiling was a miracle of particle physics. Turning on a radio and looking it's back side lead to a warm glow and made you feel like in a 1900s scientist. Then the radio blinked at you with its green eye.... OK OK.... I've got nostalgic... no way a bloody tiny square lump of plastic IC will make that.
Aluminization is a more complex procedure than you might realize. It adds several extra steps to the manufacture of a CRT and causes shrinkage which means the entire bulb has to be rewashed and the screening process started all over again. Tubes that were smaller, such as in some of the first portables around 1956, were not aluminized to cut cost and a bright picture was secondary to the cost of the set.
The light reflective effect that made the image brighter was the first reason aluminizing was used. I think that realizing the ion burn reduction was also a benefit was later. There are CRT used in the mid 50s that were aluminized and still use an ion trap magnet. Could also be that there were a lot of guns in stock that required an ion trap so they wanted to use them up.
In the UK we were always advised to make sure your tube had and ion trap, when aluminized screens came along everyone still asked for an ion trap so we ended up with tubes with an ion trap that were also aluminized.
True. The first generation 21ALP4A was aluminized with a bent gun and ion trap. On that tube, only the rear 1/3 of the cone had the dag coating, the rest was uncoated, so you could see the aluminum inside. Admiral introduced these into their lineup in the 1956 model year with the new 18Y4, 18SY4, 19Y4, 19SY4, 20Y4, and 20SY4 chassis of their Advanced and Super Cascode series. The selling point was that you could comfortably watch TV without dimming the lights. I grew up with one of those sets and we never once dimmed our lights. The later generation 21ALP4B had a straight gun and raised the anode to 21kV, the earlier tubes ran at 16kV.
The electrons are accelerated by DC EHT however they are modulated by AC to provide the image. I suspect the real answer involves complex maths and quantum physics relating to how energy is converted from the mass of the electrons to photons of light These posts have been so interesting thank you very much. I love the vintage picture and ads also.
Thanks for the videos. The CRT is indeed an amazing product of engineering and physics! This seems like a good place to ask a question about a CRT issue. I have a 10BP4 that has a very persistent G1 short as it warms up. I am unable to remove it with 2 different testers I have. I do have a replacement but wonder if trying to blast it with a large external capacitor might work. Any thoughts? I am restoring a Philco 49-1040 TV and looking forward to following along with you when you restore yours.
There may be a particle between the G1 and G2 which doesn't show up until the G1 heats and "oil cans." Leave it on the tester for several minutes to let everything heat and expand, then try short removal.
I believe that's exactly what the clear short function does in the testers. If you do try an external cap, you can experiment with voltage and cap size though so it might work better.
Insightful video!...GE-Techni-Talk from October 11, 1953 provides some detail on the process to manufacture an aluminized picture tube…the aluminum coating is condensed onto the back of the phosphor coating as well as the walls of the bulb…the complex part seems to be associated with laying an extremely thin layer of plastic over the phosphor to protect it, which is then baked out after the aluminum is deposited…could have been a low yield process with rejects and limited production numbers!!...also aluminized tubes would have been a competitive advantage for GE, RCA, Sylvania in their sets…selling non-aluminized tubes to other manufacturers, while selling aluminized replacement picture tubes to a booming aftermarket may have maximized profit…you never know!!!
5:27 They are following the aquadag to the ultor connection through the high voltage lead through the rectifier through the high voltage winding and back to ground. That's why the high voltage varies with beam current. The Beam current is the leakage of the secondary accelerating anode and the cathode current. My understanding, but I think I'm correct.
How does it get to the aquadag on the interior? There is a pretty big gap between the phosphor and the interior dag. Electrons hit the phosphor and then?
@@bandersentvif the CRT is aluminized, there is no gap as everything is conducting. But even without a conductor, you have secondary electron emission from the phosphor and also repulsive forces between them. If for whatever reason the electron is not attached to the phosphor atoms it will start being attracted by the anode just as it happened when it was originally emitted by the cathode. If it went all the way back to front it can certainly travel a few inches towards the closest area of the anode.
@@bandersentv I think the secondary electron effect is important. Electrons emitted from the spot hit by the beam from the gun. There could be some leakage also. Aluminizing could be a major conduction path in tubes with it.
@@bandersentv Always talking about non aluminized screens here. Any electron that is not captured by an atom at the screen, be it because it is a secondary emission electron, or because it has been thermally/spontaneously reemited from the phosphor, or because it has somehow lost its kinetic energy for whatever reason and not attached to an atom, is just sitting there, dislodged, "floating", feeling the acceleration from the anode. It will indeed start accelerating towards it even from the center of the screen (just as it initially accelerated from the cathode, remember that the thermal emission does not give it too much velocity, it gives it just enough to dislodge it from the cathode surface). So the distance to cover is not a problem for it (it just determines the time it takes for it to finally close the circuit), and the direction of motion should be parallel to the screen, as the sides of the tube are the nearest point to the center of the screen. So that "cloud" of returning electrons will crawl over the screen, and will indeed interfere (repel) the new incoming electrons only as they get very close to the screen, at the last instant. Those incoming electrons have a ton of velocity/inertia so they should not be terribly affected, but the image may still loose some focus. The effect might be more noticeable based on the CRT size, the amount of electrons flooding the screen (beam current) and the HV (kinetic energy of the incoming electrons). I bet they played with those values a lot when designing the TVs. I recall reading about this eons ago, but it was some obscure effect that as aluminized screens came up, simply nobody continued talking about. What I was totally unaware was that non aluminized CRTs stood around for a decade! I just assumed that everyone would have quickly depleted stocks and switched. I smell some patents and royalties there...
From my understanding the electrons that hit the phosphor lose most of their energy and velocity upon impact and therefore can be absorbed by the positively charged coating on the inside of the CRT
I think this could be considered secondary emission. The electrons hit the screen so hard they bounce off and are then attracted to the anode coating which is positively charged.
I think, from memory, that aluminized CRTs require a somewhat higher EHT than non aluminized. The electrons needed to be above a certain velocity to penetrate the aluminium layer. That could be the reason that it took a long time for the technique to become general.
AFAIK you need almost 3kV to start to light up an aluminized CRT but a non-aluminized CRT can produce light below 250v. In practice it doesn't matter because at those in-between voltages the picture is way too dim to be watchable even in a perfectly dark room.
@eDoc2020 typically non aluminized CRTs run on 9-12,000 volts so really not an issue. The early aluminized CRTs were designed to be drop in replacements. Like 10FP4 for a 10BP4
I also suspect the original aluminization process was labor intensive to apply correctly. To get a uniform thin aluminum coating, a refined process with special machinery had to be developed to maximize performance while minimizing costs. All this likely took some time to work out, which may account for the time before aluminization became the industry standard.
I think the emitted electrons strike the phosphor, displacing an electron in the phosphor atoms, which is emitted as a photon. The particulate form of a photon is an electron. The ‘wave’ form of an electron is a photon.
no, you have that wrong. Photons are exchange particles (bosons) in the electromagnetic field. The electron can gain or loose energy, emitting or absorbing photons. But it does not disappear, an electron is a stable fundamental particle, it will not decay into something else by itself (not counting electron position collision because that is an interaction). So it's not that an electron converts into a photon, travels, and then converts back into an electron or something like that. Answering, the electron stays in the screen eventually being attracted to the anode. Now... part of what you described is correct, secondary electron emission. Sometimes the phosphor atoms hit by the electron will themselves lose an electron, that electron being attracted to the anode as well, while the initial electron takes its place there, having lost is kinetic energy. The CRT is a beautiful example of a particle accelerator.
not sure if I was clear enough... and answering on the cell phone is a pain. the point is that the kinetic energy of the electron gets converted to a photon, but the electron remains, just with a lower energy.
It's impossible to recreate a vacuum tube, but I don't think it would be possible with the oxidized metal material of an electron gun, but I thought about it as well.I think it's difficult, but I'm looking forward to playing it like music on a cathode ray tube.
![KSI - Dirty [Official Visualiser]](http://i.ytimg.com/vi/VoDh1h1dPUE/mqdefault.jpg)
The beam current return path is back through the second anode. On aluminized tubes, the aluminum layer is connected to the second anode coating. On older non-aluminized tubes, the screen and phosphor itself builds up a considerable static charge, which slowly leaks across the glass (or through whatever contaminants are on the surface) back to the coated portion of the bulb. The static charge buildup on the phosphor can cause a phenomenon called "image sticking", where the image persistence starts becoming longer, and blurs details. This acts as a severe limitation of the accelerating potential, and consequently image brightness. Aluminizing the tubes was a great advance with 3 major improvements. Prevents phosphor damage from ion bombardment, reflecting light emitted from the backside of the phosphor screen in a forward direction (major brightness increase), and eliminates image sticking by providing an easy return path for the beam current. This allows the use of higher accelerating voltages, and even better image brightness.
I'd like to add something. Others and I have added a few answers here and there, so we can say the return path for the electrons is clear. Now, there is an interesting spin to this. There is a special case of CRTs, in which you indeed are interested in the electrons remaining as buildup charge. You see, the electron looses its kinetic energy when it hits the screen (be it into phosphor atoms, into lacquer coating atoms, or even glass). It obviously doesn't disappear. So the anode will start accelerating those electrons again, this time to the sides, in a motion parallel to the screen.
Now, as the electron had no motion to start with, it will take time to accelerate, meaning the glass area will retain that static charge buildup for some time before it gets into the anode again. And "If it takes time... it's MEMORY".
Regular oscilloscope CRTs were used as Williams-Kilburn memory tubes in early first generation computers. You simply needed a conducting faceplate at the outer face of the screen to sense that charge buildup, instead of your finger. And that provided a better return path (capacitive) than the HV anode. The charge would go away in a fraction of a second, but you could scan, read, write again, before it would vanish.
But the anode potential was still there, complicating things because as electrons moved sideways they would eventually spill from a charged 1 area into an uncharged 0 area causing memory retention problems.
As the 1950s progressed, specialized tubes were made like RADECHONS and other storage tubes, with the sensing faceplate inside the glass envelope, and usually with a wire mesh that isolated the buildup charge from the anode eliminating the spill problem, seriously raising the retention.
And with an entire decade of research and funding, with things finally ready for a reasonably good computer memory, An Wang developed tiny magnetic cores, giving way cheaper, lifetime retention, binary memory with a rather simple binary addressing system... the storage tubes evaporated in the blink of an eye.
Almost... because storage CRTs were able to retain ANALOG charge levels... not only binary.
So they remained in a plethora of niche applications. The soviets used them in their radars up to the 80s! They were used as a memory to take a baseline and spot the difference (moving target) between two consecutive radar scans.
Also scan converters of the 60s used these weird CRT contraptions, with one electron beam to one side, doing the writing and another to the other side of the screen doing the reading.
The latest modern storage tube I am aware of, is a weird Tektronics storage/digitizing CRT (without a visible screen) which was used in some GHz oscilloscope I don't quite remember, I think in the 1980s. The scope had a regular CRT for its screen, and this weird thing inside to do the hard work.
Physics is beautiful, and in those days you had these particle accelerators right there in front of your eyes, which you could play with in your garage. Every fluorescent tube in a ceiling was a miracle of particle physics. Turning on a radio and looking it's back side lead to a warm glow and made you feel like in a 1900s scientist. Then the radio blinked at you with its green eye....
OK OK.... I've got nostalgic... no way a bloody tiny square lump of plastic IC will make that.
Never tire of CRT chat.
Aluminization is a more complex procedure than you might realize. It adds several extra steps to the manufacture of a CRT and causes shrinkage which means the entire bulb has to be rewashed and the screening process started all over again. Tubes that were smaller, such as in some of the first portables around 1956, were not aluminized to cut cost and a bright picture was secondary to the cost of the set.
The light reflective effect that made the image brighter was the first reason aluminizing was used. I think that realizing the ion burn reduction was also a benefit was later. There are CRT used in the mid 50s that were aluminized and still use an ion trap magnet. Could also be that there were a lot of guns in stock that required an ion trap so they wanted to use them up.
In the UK we were always advised to make sure your tube had and ion trap, when aluminized screens came along everyone still asked for an ion trap so we ended up with tubes with an ion trap that were also aluminized.
True. The first generation 21ALP4A was aluminized with a bent gun and ion trap. On that tube, only the rear 1/3 of the cone had the dag coating, the rest was uncoated, so you could see the aluminum inside. Admiral introduced these into their lineup in the 1956 model year with the new 18Y4, 18SY4, 19Y4, 19SY4, 20Y4, and 20SY4 chassis of their Advanced and Super Cascode series. The selling point was that you could comfortably watch TV without dimming the lights. I grew up with one of those sets and we never once dimmed our lights. The later generation 21ALP4B had a straight gun and raised the anode to 21kV, the earlier tubes ran at 16kV.
The electrons are accelerated by DC EHT however they are modulated by AC to provide the image. I suspect the real answer involves complex maths and quantum physics relating to how energy is converted from the mass of the electrons to photons of light These posts have been so interesting thank you very much. I love the vintage picture and ads also.
Thanks for this. More of this kind of info, please.
Thanks for explaining this very helpful thanks Mike
Thanks for the videos. The CRT is indeed an amazing product of engineering and physics! This seems like a good place to ask a question about a CRT issue. I have a 10BP4 that has a very persistent G1 short as it warms up. I am unable to remove it with 2 different testers I have. I do have a replacement but wonder if trying to blast it with a large external capacitor might work. Any thoughts? I am restoring a Philco 49-1040 TV and looking forward to following along with you when you restore yours.
There may be a particle between the G1 and G2 which doesn't show up until the G1 heats and "oil cans." Leave it on the tester for several minutes to let everything heat and expand, then try short removal.
I believe that's exactly what the clear short function does in the testers. If you do try an external cap, you can experiment with voltage and cap size though so it might work better.
Insightful video!...GE-Techni-Talk from October 11, 1953 provides some detail on the process to manufacture an aluminized picture tube…the aluminum coating is condensed onto the back of the phosphor coating as well as the walls of the bulb…the complex part seems to be associated with laying an extremely thin layer of plastic over the phosphor to protect it, which is then baked out after the aluminum is deposited…could have been a low yield process with rejects and limited production numbers!!...also aluminized tubes would have been a competitive advantage for GE, RCA, Sylvania in their sets…selling non-aluminized tubes to other manufacturers, while selling aluminized replacement picture tubes to a booming aftermarket may have maximized profit…you never know!!!
as spock says (Star Trek) fascinating😊
5:27 They are following the aquadag to the ultor connection through the high voltage lead through the rectifier through the high voltage winding and back to ground. That's why the high voltage varies with beam current. The Beam current is the leakage of the secondary accelerating anode and the cathode current. My understanding, but I think I'm correct.
How does it get to the aquadag on the interior? There is a pretty big gap between the phosphor and the interior dag. Electrons hit the phosphor and then?
@@bandersentvif the CRT is aluminized, there is no gap as everything is conducting. But even without a conductor, you have secondary electron emission from the phosphor and also repulsive forces between them. If for whatever reason the electron is not attached to the phosphor atoms it will start being attracted by the anode just as it happened when it was originally emitted by the cathode. If it went all the way back to front it can certainly travel a few inches towards the closest area of the anode.
@TheAlchaemist I was think of electrons closer to the center of the screen
@@bandersentv I think the secondary electron effect is important. Electrons emitted from the spot hit by the beam from the gun. There could be some leakage also. Aluminizing could be a major conduction path in tubes with it.
@@bandersentv Always talking about non aluminized screens here. Any electron that is not captured by an atom at the screen, be it because it is a secondary emission electron, or because it has been thermally/spontaneously reemited from the phosphor, or because it has somehow lost its kinetic energy for whatever reason and not attached to an atom, is just sitting there, dislodged, "floating", feeling the acceleration from the anode. It will indeed start accelerating towards it even from the center of the screen (just as it initially accelerated from the cathode, remember that the thermal emission does not give it too much velocity, it gives it just enough to dislodge it from the cathode surface).
So the distance to cover is not a problem for it (it just determines the time it takes for it to finally close the circuit), and the direction of motion should be parallel to the screen, as the sides of the tube are the nearest point to the center of the screen.
So that "cloud" of returning electrons will crawl over the screen, and will indeed interfere (repel) the new incoming electrons only as they get very close to the screen, at the last instant. Those incoming electrons have a ton of velocity/inertia so they should not be terribly affected, but the image may still loose some focus. The effect might be more noticeable based on the CRT size, the amount of electrons flooding the screen (beam current) and the HV (kinetic energy of the incoming electrons). I bet they played with those values a lot when designing the TVs.
I recall reading about this eons ago, but it was some obscure effect that as aluminized screens came up, simply nobody continued talking about.
What I was totally unaware was that non aluminized CRTs stood around for a decade! I just assumed that everyone would have quickly depleted stocks and switched. I smell some patents and royalties there...
From my understanding the electrons that hit the phosphor lose most of their energy and velocity upon impact and therefore can be absorbed by the positively charged coating on the inside of the CRT
Make sense but I'm curious if they interfere with the electrons coming towards the screen. Seems like they would form a cloud above the screen
I think this could be considered secondary emission. The electrons hit the screen so hard they bounce off and are then attracted to the anode coating which is positively charged.
I think that is a good explanation. There could be other effects such as a conductive path in aluminized tubes.
I would like to see inside one of those picture tubes.
I think, from memory, that aluminized CRTs require a somewhat higher EHT than non aluminized. The electrons needed to be above a certain velocity to penetrate the aluminium layer. That could be the reason that it took a long time for the technique to become general.
They are interchangeable but aluminized can handle higher EHT allowing for an even brighter image.
AFAIK you need almost 3kV to start to light up an aluminized CRT but a non-aluminized CRT can produce light below 250v. In practice it doesn't matter because at those in-between voltages the picture is way too dim to be watchable even in a perfectly dark room.
@eDoc2020 typically non aluminized CRTs run on 9-12,000 volts so really not an issue. The early aluminized CRTs were designed to be drop in replacements. Like 10FP4 for a 10BP4
I wonder if the aluminized process was patented and no one wanted to pay the patent fees?
OK, but for example GE had some of the first aluminized CRTs and they only used them in some models.
I also suspect the original aluminization process was labor intensive to apply correctly. To get a uniform thin aluminum coating, a refined process with special machinery had to be developed to maximize performance while minimizing costs. All this likely took some time to work out, which may account for the time before aluminization became the industry standard.
@bandersentv It would be interesting to look up the first patent on this. Was it GE or some other person or company not directly making picture tubes?
I think the emitted electrons strike the phosphor, displacing an electron in the phosphor atoms, which is emitted as a photon. The particulate form of a photon is an electron. The ‘wave’ form of an electron is a photon.
no, you have that wrong. Photons are exchange particles (bosons) in the electromagnetic field. The electron can gain or loose energy, emitting or absorbing photons. But it does not disappear, an electron is a stable fundamental particle, it will not decay into something else by itself (not counting electron position collision because that is an interaction). So it's not that an electron converts into a photon, travels, and then converts back into an electron or something like that. Answering, the electron stays in the screen eventually being attracted to the anode. Now... part of what you described is correct, secondary electron emission. Sometimes the phosphor atoms hit by the electron will themselves lose an electron, that electron being attracted to the anode as well, while the initial electron takes its place there, having lost is kinetic energy. The CRT is a beautiful example of a particle accelerator.
not sure if I was clear enough... and answering on the cell phone is a pain. the point is that the kinetic energy of the electron gets converted to a photon, but the electron remains, just with a lower energy.
@@TheAlchaemist indeed, a particle accelerator that used to be in every home, and even a mass spectrometer if old enough to have an ion trap.
Im first
but are you aluminized?
It was removed
Very painful
It's impossible to recreate a vacuum tube, but I don't think it would be possible with the oxidized metal material of an electron gun, but I thought about it as well.I think it's difficult, but I'm looking forward to playing it like music on a cathode ray tube.