If that resistor at the bottom of the eye tube socket goes high in value it will also produce a dim display. In older USA sets that resistor is hidden in the tube socket and is often missed being replace (or checked) by inexperienced restorers. Interesting video thanks for sharing.
Thanks for covering this, its a good topic. I have played around with the North American versions, with the round arc (6E5 and compatible). One tactic that I have seen used in the past was to increase the *heater voltage* to increase the pool of electrons around the cathode. I have a couple of radio projects coming up using magic eye tubes (NOS) and I have decided that I will try to modify the circuit on them to deliberately cut down the heater voltage initially. The idea here is to lessen the brightness on a NOS tube to increase its usable lifetime. I tested this idea and it looks feasible; the NOS tubes are pretty bright at the designed heater voltage. I was planning on adding a bypass switch to restore the full heater voltage when it eventually gets to the point where the lower voltage is not bright enough. One possible improvement to that idea might be to add a circuit (new PCB, yay!) to temporarily brighten the display when the radio is being tuned and then cut the heater voltage when the tuning is fixed & set. Cheers,
According to Ludwill Sibley, author of the excellent reference book "Tube Lore", age-related dimming of 6E5 and 6U5 tubes is primarily caused by "contamination" of the green- florescing coating on the cathode, which he referred to as "willemite". (I assume that something cooking off from the tube elements eventually contaminates the willemite). He wrote in the book that experiments at rejuvenation of those particular eye tube types, by members of his radio club, had largely failed or been inconclusive. If course, the later eye-tubes such as EMM801, EM 84 and such may use different phosphors or coatings. Either way, it can't hurt to try! The only tube types I ever had any success at rejuvenating were a batch of early tubes with thoriated did tungsten filaments. I forget if it was WD11's or 199's, I think it was the 199's. The procedure was in Sibley's book, and further details were found on line.
@john beach Somewhere I read an article from a radio collector who had installed a small step up power supply (a pulse width or switching circuit, IIRC) to bump up the heater voltage to 12V so that he could use a much cheaper 1629 eye tube; this also likely requires other circuit adjustments or mods.....
Interesting experiment ! I have sometimes toyed with the idea of using a switch to cut off the B+ when I want to do some extended listening and there is nobody around to 'wow'.
I have done exactly this on an old tube radio with a UM4 magic eye tube. Those tubes are like £50 a piece and getting hard to find. I used a DPDT switch to switch off B+ for the tube and switch between the filament or a 5W resistor that drops as much voltage as the resistor does. You'll need a switch which is rated for DC (and in my case tested at 250V DC). These aren't particularly cheap, and there aren't many choices. Switching DC is not as simple as AC as it arcing much more.
I usually use 275-300 volts B+ on the EM84/6E2 Magic Eye tubes that I use in my D.I.Y. projects, and they're PLENTY bright at that level, and YES, you are correct in that one WILL have to alter their drive voltage if they increase the B+ in an already existing circuit.
Thank you As a comment below says magic eyes are small cathode ray tubes. I think the problem is ion burn which happened in early television tubes before they started putting a thin aluminium film at the back of the phosphor. TV crt’ s certainly lasted more than 1000 hours. I’ve read elsewhere that reducing the target voltage increases magic eye life. Manufacturers liked to have the magic eyes bright this apparently was good for sales. Also no magic eyes have aluminised backing on the phosphor because most have a target hit by the electrons on the front and while the EM84 is backlit I’m sure the cost would deter this protection Just sell more tubes. People are trying perfect led copies of magic eye tubes but so far not.
One last shot you can give them if the phosphor layer doesnt seem too burnt is to slowly increase filament voltage to 175% and then give the target a few short 2 second blasts at about 350v, then decrease filament voltage again. Dont do this for more than a few minutes. If the cathode has gone sleepy or poisoned this will wake it right up again. Had this on some brand new 6AF6, worked very well.. The one in the video, mind you, is deader than a doornail. Evident when you see the target. I once heard this was apparently due to the heavy ion bombardment breaking up the Zn2SI04 molecule chain, thus reducing the Zinc back to the metallic state and liberating the Oxygen molecules which get absorbed by the getter, which would in turn explain the darkened (burnt) patches...
You also play around with the heater supply. For the magic eye valves I've used, sometimes the heater current drops off with age and by increasing the heater voltage to a point where the recommended current should be, you can also get more life out of them. I know it's a bit of a faf to find 7.5V (for example) instead 6.3V, but it can be done with a handful of components.
I wonder whether it's a loss of vacuum issue or if the phosphor has decayed? I wonder how hard it would be to melt a new new tube stem to the end, re-pull the vacuum and reseal it? The indicator on the end would turn white tho.
Greetings: The tuning eye will last much longer if only powered when actually "tuning". I propose using a combination of 555 timer and a reed relay to remove the HT to the tube when not actually tuning. The timer will be triggered on at the start of tuning and time out a selected. I suggest an integrated AVC detector to monitor AVC level and trigger when an AVC level change is detected. What do you think?
Because the phosphor target on this type of tube is so large compared to a 6E5 and the like, how about a weak magnet to steer the beam onto the un-burned portion?
Was the current draw of the new one any higher than the spent one at the same voltage? I think if the cathode material was spent, the current would be much lower. You could make a voltage doubler circuit fed directly from the B+ secondary of the mains transformer. Just two silicon diodes and two low value capacitors and a resistor. You could change the 470K triode resistor to 1M just to keep the triode voltage lower. Few years ago I played with a bench power supply that goes to 600V and some dead magic eyes, EM34s and EM80/84s. At higher voltages they started to shine again, but they usually needed like 450V-500V to be useful, but some that still had some life left were quite happy at just 50-100V more than their usual B+. In essence, what are you seeing is the same as the burn-in on the face of CRT screens. Also I remember that increasing filament voltage made little or no difference in brightness. That being said a friend of mine built a one tube reaction radio receiver back in the early 1950s with a spent magic eye tube. He used the triode as an amplifier and it worked since the tube itself was not "spent", but just the phosphorus layer.
It was worth a try but as you said, the tube is pretty much shot so would need replacing anyway. As a bodge to get a set out of the door if the customer won't spend money it is ok but it will die even quicker.
I been following you for a short time ,Do,you ever work on American tube radios, 120 volt sets or tube dc powered sets ? You do work on some pretty cool radios .
Interesting experiment, thanks. I plan to add a magic eye to a no-name 1951 kit radio that never had one. Experiments like this are therefore useful learning experiences. I wonder, though, could rebiasing the signal input bring the two bars closer together where there might be some unburnt phosphor to play with, or will the physical plate dimensions prevent that?
Greetings: Regardless of the method you select to improve the display, I have a valid method to extend the life of that display. That is to limit its use to only when tuning is being done. I propose using a relay or electronic switch to disable the high target voltage after a timeout period set with a 555 timer or similar. The timer can be triggered either manually with a momentary push button or automatically by sensing a change in the AVC voltage or change in the local oscillator frequency. I am not that good a circuit designer to suggest an appropriate circuit to monitor either sense source. A method not often available on vintage radios is the pulsing of a shaft encoder used to change the volume or frequency setting.
I have quite a few tube radios a few have the tuning eye it's totally awesome. My zenith 9s 262 has a tuning I as well as a model that I just picked up that's going to be restored.
As the new valve was so bright might be worth lowering the voltage (and brightness) a little to extend the life. It is after all a CRT and we all know the damage you can do with burn on a Scope with an over bright image! Any experience with some of the overseas cheaper magic eyes? Will probably need a small re wire but could be a suitable replacement.
I do wonder if phosphor depletion / Coulomb ageing / "wearing out" isn't the whole story, or at least only one of several different reasons why magic eye valves degrade. My reasoning: On your EM84, notice that the outer and inner edges are considerably brighter than the rest (presumably due to something like internal reflections increasing the # of electrons hitting the phosphor). If it was simply the phosphor 'wearing out', you'd expect the outer edges (that are active continuously) to wear out first/most, followed by the inner edges (that are getting a double-dose of electrons whenever tuned to a strong signal i.e. most of the time), and the gap between (that are only getting a 'normal' dose of electrons, and only when tuned) being finally/least affected. But yours (and the others few of that type I've seen; magic eyes not being common except on mostly Euro personally imported sets here in Aus) shows the opposite - the edges bright, and the centre dull. That said, I have seen other styles - mostly round dial-types like the 6E5 & friends - where the degradation is more pronounced in the 'overlap' area, presumably from being run for a long time while tuned to a strong signal. So I suspect there's several causes - Coulomb ageing/wearing out, reduced cathode emission (did they use particularly high-emission cathode material? Don't know…), and likely others. Interestingly, I've also seen it stated somewhere (probably a discussion on RM) that brightness increases with anode voltage but is not linear (e.g. 20% higher anode voltage results in more than a 20% increase in brightness), while on the other hand, degradation increases with lower voltages and higher currents but decreases with higher voltages and lower currents. Given that boosting worn magic eyes by increasing the anode voltage (and hence, without changing anything else, also increasing cathode current) is known to work but significantly reduces remaining lifespan, I wonder if a combination of increasing the anode voltage and also decreasing cathode current (e.g. adding resistance to the cathode if possible) would extend the life of 'rejuvenated' valves? (You mentioned a video or two ago you tend to ramble on & drag things out. Yeah, I'm like that in comments 😉)
Hi Jim. I too was mystified by the bright lines at the two ends of the beam travel. My guess is that these limits act as a sort of “trap” for the burnt off phosphor, but that’s just a guess. The physics is rather interesting, and I’ve read quite a bit about it. However, as an engineer, I can’t help but remember what one of my varsity lecturers used to say: “leave the theory to the physicists, and just get in with the job”. I must admit that I often break this rule due to my curiosity, but in this case, I think I’ll leave it there :) As for rambling on, I really don’t mind. I alway preferred conversations to presentations, so we’re both in that habit. Thanks for your input. Manuel
Simon Spiers : the weird thing Simon, is that I’ve actually read somewhere that a lower anode voltage burns the layer even faster. Doesn’t make sense to me though.
Ich wollte Wissen ob ich die 6E2 ersetzen kann durch eine EM800. Ist der Sockel gleich und die Pinn Belegung. Oder muss die Platine angepasst werden? Oder geht es gar nicht? Danke I wanted to know if I could replace the 6E2 with an EM800. Is the socket the same and the pin assignment. Or does the board have to be adapted? Or is it not possible at all? Thank you
@@electronicsoldandnew Danke. Ich kaufe mir nächsten Monat welche. Und berichte Dir dann. Grüsse aus Germany 🇩🇪 / Thank you. I'll buy some next month. And then report to you. Greetings from Germany 🇩🇪
Could also drive the electrode with more negative differential to close the gap more which will move the cathode emission into new territory but sadly the burnt out area of phosphor will still glow just as weak as before.
I remember when you could get "tube brighteners" that cranked up the heater voltage on a TV CRT from 6.3 to maybe 8. They were a small autotransformer with attached adapter plug and socket. You could plug it right on in seconds. Better than buying a new CRT.
@@electronicsoldandnew those were to try to increase cathode emission in worn out crts cathode coating , in the case of magic eyes its worn out phosphor thats the problem, not cathode emission,
You can use a voltage doubler using 2* IN4007 and 2* 450 volt capacitors 10 micro farads and a 100 ohm safety resister in series.1 guy i read about runs theses old 6g5,6u5 etc close to 1000 volts.
you might want to decrease the voltage maybe the filament voltage, on the new tube so the tube will last longer. This is a try and see I am not an expert. scopes and TV's have brightness control. you should have the the tube just bright enough to tune the radio. it's a tuning indicator not a show light. 73
It's funny, whenever Americans talk about magic eye tubes, it's always the kind I've never seen with something like a pie-chart right in the top of the tube. (6E5???) But whenever I see one in European kit (my old Phillips and Stellaphone tape recorders had these), it's like the one you show here. Has anyone got any idea as to why different continents had different magic eyes... or is it just an error in my perception? ;)
Was looking at these last week (UK Ebay)and you could get 10 for £20.00 delivered (includes postage) from China, mine in my Philips is OK and have a new spare but was tempted to buy.Interesting video and you are right some of those magic eye valves are mega expensive. PS I still disagree about reforming filter caps, there old there old.:):)
@@electronicsoldandnew Well here's the link and unless I am missing something it does seem a good deal. www.ebay.co.uk/itm/10pcs-Magic-Eye-6E2-EM87-EM84-Tube-Audio-Indicator-tube-tube-AMP-DIY/283131268505?hash=item41ebf04d99:g:0k8AAOSwYxdbh~fW
@@electronicsoldandnew as for caps, i have lots of old electronic equipment and the majority still have their original electrolytics in as they were ok as is or reformed ok😉 they can last much longer than many people think but obviously its very variable, biggest problem is heat and ripple current,
There’s a great article in radiomuseum about reviving magic eyes by doubling the voltage. The article suggests that it is current rather than voltage that causes degradation. www.radiomuseum.org/forum/lighting_up_dark_eye_tubes.html A schematic Is provided for a voltage doubler, this would make a GREAT video :) They even suggest that the voltage doubler design will increase the life of a new magic eye. You would understand their logic far better than me I’m sure, they also reduce heater voltage. Regards Kevin
I just found another take on a magic eye replacement in the ac7zl youtube channel. This is a combination of mechanical vision and solid state control and it's just brilliant. The realisation needs some refinement but it already looks very good. th-cam.com/video/QFTDOZz-LlE/w-d-xo.html The website is called hpfriedrichs where the details are given. I think the natural progression of this is some kind of round l.c.d. screen controlled by a tiny programmable controller. In most cases, a square screen is equally applicable since the magic eye usually protrudes through a round hole on the front of the radio/instrument.
@@electronicsoldandnew they used to 'regun' crts, so should be possible to replace the phosphor screen in these, and regetter and revacuum ..? the 'white line' type phosphor seems to last longer than the 'grey' stuff as used in em34s, etc, so maybe could use this, i've even had an em34 with a 'white' phosphor coated display disk, but stupidly didnt keep it but sold it in a radio. also seen white coated em85, still have that one!
When a magic eye tube has gone, it's gone. For the price of a new or NOS EM84 I wouldn't bother trying to turbocharge it. If the set has an EM34/35 then I replace it with a Russian 6E5C
Running it 10 to 15 percent over max recommended voltage shouldn’t be a problem as the tube is aged and at the end of its life anyway. What could it hurt. Sure wish there was a 350 volt tap 🤣
Have you seen Gord Rabjohn's solid state replacements? th-cam.com/video/T6HPaSh0j1o/w-d-xo.html The weak point of his round magic eye (the proper magic eye) replacement is the use of a diffuser. I think that a plastic prismatic light guide with a reflective coating would work a lot better if one took the time to build one. For linear magic eyes however, neither a diffuser or any light guide are necessary and his idea is more easily amenable to this type.
@@electronicsoldandnew How does he get the diodes soldered? Does he order the boards already populated? Also I suggested that if the diodes were arranged vertically, it would allow for tighter packing together and hence would not need a diffuser except I forgot the slight issue of the need for a cylindrical board in order to achieve that...
@@electronicsoldandnew I did but I'll visit it again. I just found out that pcbway gives the option to order aluminium boards. It also allows one to order flexible boards. I wonder what these are like and whether they can withstand the heat from the diodes.
Click baiting is really not a tactic that I give any thought to. If you see the video you’ll realise that picture is an actual shot from the video. It takes long enough to make these videos without worrying about how best to bait anyone. I almost always just take a shot from my actual video and make the thumbnail.
@@electronicsoldandnew I did see the video. At the end didn't you replace the old tube with a new one and isn't that new one the one pictured in the thumbnail?
its trying to squeeze a bit more light out of it 😉 i dont think it can be revived, if the phosphor is worn,, low cathode emission may be able to be 'kicked' a bit by doing similar to crt 'rejuvenation',
If that resistor at the bottom of the eye tube socket goes high in value it will also produce a dim display. In older USA sets that resistor is hidden in the tube socket and is often missed being replace (or checked) by inexperienced restorers. Interesting video thanks for sharing.
I check it always, because I’ve often found it going up in value. Thanks.
Thanks for covering this, its a good topic.
I have played around with the North American versions, with the round arc (6E5 and compatible). One tactic that I have seen used in the past was to increase the *heater voltage* to increase the pool of electrons around the cathode.
I have a couple of radio projects coming up using magic eye tubes (NOS) and I have decided that I will try to modify the circuit on them to deliberately cut down the heater voltage initially. The idea here is to lessen the brightness on a NOS tube to increase its usable lifetime. I tested this idea and it looks feasible; the NOS tubes are pretty bright at the designed heater voltage. I was planning on adding a bypass switch to restore the full heater voltage when it eventually gets to the point where the lower voltage is not bright enough.
One possible improvement to that idea might be to add a circuit (new PCB, yay!) to temporarily brighten the display when the radio is being tuned and then cut the heater voltage when the tuning is fixed & set.
Cheers,
Sounds interesting. Good luck
According to Ludwill Sibley, author of the excellent reference book "Tube Lore", age-related dimming of 6E5 and 6U5 tubes is primarily caused by "contamination" of the green- florescing coating on the cathode, which he referred to as "willemite". (I assume that something cooking off from the tube elements eventually contaminates the willemite). He wrote in the book that experiments at rejuvenation of those particular eye tube types, by members of his radio club, had largely failed or been inconclusive. If course, the later eye-tubes such as EMM801, EM 84 and such may use different phosphors or coatings. Either way, it can't hurt to try!
The only tube types I ever had any success at rejuvenating were a batch of early tubes with thoriated did tungsten filaments. I forget if it was WD11's or 199's, I think it was the 199's. The procedure was in Sibley's book, and further details were found on line.
@john beach Somewhere I read an article from a radio collector who had installed a small step up power supply (a pulse width or switching circuit, IIRC) to bump up the heater voltage to 12V so that he could use a much cheaper 1629 eye tube; this also likely requires other circuit adjustments or mods.....
Interesting experiment ! I have sometimes toyed with the idea of using a switch to cut off the B+ when I want to do some extended listening and there is nobody around to 'wow'.
I have done exactly this on an old tube radio with a UM4 magic eye tube. Those tubes are like £50 a piece and getting hard to find. I used a DPDT switch to switch off B+ for the tube and switch between the filament or a 5W resistor that drops as much voltage as the resistor does. You'll need a switch which is rated for DC (and in my case tested at 250V DC). These aren't particularly cheap, and there aren't many choices. Switching DC is not as simple as AC as it arcing much more.
You'd better turn off the filament as well.
So, you can squeeze a bit more juice out of it. That's nice. One can do that on his own radio. Thanks for sharing.
I usually use 275-300 volts B+ on the EM84/6E2 Magic Eye tubes that I use in my D.I.Y. projects, and they're PLENTY bright at that level, and YES, you are correct in that one WILL have to alter their drive voltage if they increase the B+ in an already existing circuit.
👍
Thank you
As a comment below says magic eyes are small cathode ray tubes. I think the problem is ion burn which happened in early television tubes before they started putting a thin aluminium film at the back of the phosphor. TV crt’ s certainly lasted more than 1000 hours.
I’ve read elsewhere that reducing the target voltage increases magic eye life.
Manufacturers liked to have the magic eyes bright this apparently was good for sales.
Also no magic eyes have aluminised backing on the phosphor because most have a target hit by the electrons on the front and while the EM84 is backlit I’m sure the cost would deter this protection Just sell more tubes.
People are trying perfect led copies of magic eye tubes but so far not.
👍
One last shot you can give them if the phosphor layer doesnt seem too burnt is to slowly increase filament voltage to 175% and then give the target a few short 2 second blasts at about 350v, then decrease filament voltage again. Dont do this for more than a few minutes. If the cathode has gone sleepy or poisoned this will wake it right up again. Had this on some brand new 6AF6, worked very well..
The one in the video, mind you, is deader than a doornail. Evident when you see the target. I once heard this was apparently due to the heavy ion bombardment breaking up the Zn2SI04 molecule chain, thus reducing the Zinc back to the metallic state and liberating the Oxygen molecules which get absorbed by the getter, which would in turn explain the darkened (burnt) patches...
i’ve got to try that. sound easy and one has nothing to lose if it fails.
most of the worn magic eyes i have, has been due to worn out phosphor, not cathode emission,
You also play around with the heater supply. For the magic eye valves I've used, sometimes the heater current drops off with age and by increasing the heater voltage to a point where the recommended current should be, you can also get more life out of them. I know it's a bit of a faf to find 7.5V (for example) instead 6.3V, but it can be done with a handful of components.
👍could simply rectify the 6.3 for this tube only.
I wonder whether it's a loss of vacuum issue or if the phosphor has decayed?
I wonder how hard it would be to melt a new new tube stem to the end, re-pull the vacuum and reseal it?
The indicator on the end would turn white tho.
Greetings:
The tuning eye will last much longer if only powered when actually "tuning".
I propose using a combination of 555 timer and a reed relay to remove the HT to the tube when not actually tuning. The timer will be triggered on at the start of tuning and time out a selected. I suggest an integrated AVC detector to monitor AVC level and trigger when an AVC level change is detected. What do you think?
That would be quite doable, but I don’t like making that many changes to the radio.
Because the phosphor target on this type of tube is so large compared to a 6E5 and the like, how about a weak magnet to steer the beam onto the un-burned portion?
Not a bad idea for a future experiment.
Was the current draw of the new one any higher than the spent one at the same voltage?
I think if the cathode material was spent, the current would be much lower.
You could make a voltage doubler circuit fed directly from the B+ secondary of the mains transformer. Just two silicon diodes and two low value capacitors and a resistor. You could change the 470K triode resistor to 1M just to keep the triode voltage lower. Few years ago I played with a bench power supply that goes to 600V and some dead magic eyes, EM34s and EM80/84s. At higher voltages they started to shine again, but they usually needed like 450V-500V to be useful, but some that still had some life left were quite happy at just 50-100V more than their usual B+. In essence, what are you seeing is the same as the burn-in on the face of CRT screens. Also I remember that increasing filament voltage made little or no difference in brightness. That being said a friend of mine built a one tube reaction radio receiver back in the early 1950s with a spent magic eye tube. He used the triode as an amplifier and it worked since the tube itself was not "spent", but just the phosphorus layer.
I really can’t recall what the current draw was. It’s been quite a while.
I did the same with a 6g5 magic eye that was 25 years ago still going fine. Went from 235 to 300 volts not as bright as new tube but it works.
👍
My most interesting project of magic eye ,I like it and wish to see the connection of EM 34 magic eye.
It was worth a try but as you said, the tube is pretty much shot so would need replacing anyway. As a bodge to get a set out of the door if the customer won't spend money it is ok but it will die even quicker.
Unfortunately, I have a problem. The customer is me! :)
I hear you with that! We try these things... if it works, great, if it doesn't, you lose nothing by trying.
I been following you for a short time ,Do,you ever work on American tube radios, 120 volt sets or tube dc powered sets ? You do work on some pretty cool radios .
I don’t get US sets over here, but I have done a few hot chassis sets.
Interesting experiment, thanks. I plan to add a magic eye to a no-name 1951 kit radio that never had one. Experiments like this are therefore useful learning experiences. I wonder, though, could rebiasing the signal input bring the two bars closer together where there might be some unburnt phosphor to play with, or will the physical plate dimensions prevent that?
Sincerely Yours : you could, but the “burnt” sections will be obvious.
Greetings:
Regardless of the method you select to improve the display, I have a valid method to extend the life of that display. That is to limit its use to only when tuning is being done. I propose using a relay or electronic switch to disable the high target voltage after a timeout period set with a 555 timer or similar. The timer can be triggered either manually with a momentary push button or automatically by sensing a change in the AVC voltage or change in the local oscillator frequency. I am not that good a circuit designer to suggest an appropriate circuit to monitor either sense source. A method not often available on vintage radios is the pulsing of a shaft encoder used to change the volume or frequency setting.
That would be quite easy to implement. However, I think many users like the tube for the look rather than for the help with tuning 😊
I have quite a few tube radios a few have the tuning eye it's totally awesome. My zenith 9s 262 has a tuning I as well as a model that I just picked up that's going to be restored.
👍
As the new valve was so bright might be worth lowering the voltage (and brightness) a little to extend the life. It is after all a CRT and we all know the damage you can do with burn on a Scope with an over bright image!
Any experience with some of the overseas cheaper magic eyes? Will probably need a small re wire but could be a suitable replacement.
I’ve replaced the em35 with a 6e5c a couple of times. Quite a simple alteration.
I do wonder if phosphor depletion / Coulomb ageing / "wearing out" isn't the whole story, or at least only one of several different reasons why magic eye valves degrade.
My reasoning: On your EM84, notice that the outer and inner edges are considerably brighter than the rest (presumably due to something like internal reflections increasing the # of electrons hitting the phosphor). If it was simply the phosphor 'wearing out', you'd expect the outer edges (that are active continuously) to wear out first/most, followed by the inner edges (that are getting a double-dose of electrons whenever tuned to a strong signal i.e. most of the time), and the gap between (that are only getting a 'normal' dose of electrons, and only when tuned) being finally/least affected.
But yours (and the others few of that type I've seen; magic eyes not being common except on mostly Euro personally imported sets here in Aus) shows the opposite - the edges bright, and the centre dull. That said, I have seen other styles - mostly round dial-types like the 6E5 & friends - where the degradation is more pronounced in the 'overlap' area, presumably from being run for a long time while tuned to a strong signal.
So I suspect there's several causes - Coulomb ageing/wearing out, reduced cathode emission (did they use particularly high-emission cathode material? Don't know…), and likely others.
Interestingly, I've also seen it stated somewhere (probably a discussion on RM) that brightness increases with anode voltage but is not linear (e.g. 20% higher anode voltage results in more than a 20% increase in brightness), while on the other hand, degradation increases with lower voltages and higher currents but decreases with higher voltages and lower currents. Given that boosting worn magic eyes by increasing the anode voltage (and hence, without changing anything else, also increasing cathode current) is known to work but significantly reduces remaining lifespan, I wonder if a combination of increasing the anode voltage and also decreasing cathode current (e.g. adding resistance to the cathode if possible) would extend the life of 'rejuvenated' valves?
(You mentioned a video or two ago you tend to ramble on & drag things out. Yeah, I'm like that in comments 😉)
Hi Jim. I too was mystified by the bright lines at the two ends of the beam travel. My guess is that these limits act as a sort of “trap” for the burnt off phosphor, but that’s just a guess. The physics is rather interesting, and I’ve read quite a bit about it. However, as an engineer, I can’t help but remember what one of my varsity lecturers used to say: “leave the theory to the physicists, and just get in with the job”. I must admit that I often break this rule due to my curiosity, but in this case, I think I’ll leave it there :)
As for rambling on, I really don’t mind. I alway preferred conversations to presentations, so we’re both in that habit.
Thanks for your input.
Manuel
I wonder if it would be reducing the Anode Voltage on the new valve to give it more life?
Simon Spiers : the weird thing Simon, is that I’ve actually read somewhere that a lower anode voltage burns the layer even faster. Doesn’t make sense to me though.
I suppose it depends whether the phosphor decays more due to current density, or more due to electron velocity (sputtering). Does anyone know?
I don’t know.
@@electronicsoldandnew there got to be a way to put a brightness control on these tube circuits. scopes and TV's have brightness controls. 73
This is a crazy thought but what if you could increase the heater voltage like a brightener does on a CRT? Would that increase the brightness?
Gerard Carriera : it could do, but would probably greatly increase the current draw, which would affect the supply voltage at that point.
Ich wollte Wissen ob ich die 6E2 ersetzen kann durch eine EM800. Ist der Sockel gleich und die Pinn Belegung. Oder muss die Platine angepasst werden? Oder geht es gar nicht? Danke
I wanted to know if I could replace the 6E2 with an EM800. Is the socket the same and the pin assignment. Or does the board have to be adapted? Or is it not possible at all? Thank you
The pinouts seem to be the same so I don’t think there would be any problem trying it. I haven’t done this myself though.
@@electronicsoldandnew Danke. Ich kaufe mir nächsten Monat welche. Und berichte Dir dann. Grüsse aus Germany 🇩🇪 / Thank you. I'll buy some next month. And then report to you. Greetings from Germany 🇩🇪
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Es Una Mini Pantalla?
I have always brightened them up by taking an HT connection direct from the cathode of the HT rectifier.
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Could also drive the electrode with more negative differential to close the gap more which will move the cathode emission into new territory but sadly the burnt out area of phosphor will still glow just as weak as before.
True
I remember when you could get "tube brighteners" that cranked up the heater voltage on a TV CRT from 6.3 to maybe 8. They were a small autotransformer with attached adapter plug and socket. You could plug it right on in seconds. Better than buying a new CRT.
Yes, that would make sense.
@@electronicsoldandnew those were to try to increase cathode emission in worn out crts cathode coating , in the case of magic eyes its worn out phosphor thats the problem, not cathode emission,
You can use a voltage doubler using 2* IN4007 and 2* 450 volt capacitors 10 micro farads and a 100 ohm safety resister in series.1 guy i read about runs theses old 6g5,6u5 etc close to 1000 volts.
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you might want to decrease the voltage maybe the filament voltage, on the new tube so the tube will last longer. This is a try and see I am not an expert. scopes and TV's have brightness control. you should have the the tube just bright enough to tune the radio. it's a tuning indicator not a show light. 73
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It's funny, whenever Americans talk about magic eye tubes, it's always the kind I've never seen with something like a pie-chart right in the top of the tube. (6E5???)
But whenever I see one in European kit (my old Phillips and Stellaphone tape recorders had these), it's like the one you show here.
Has anyone got any idea as to why different continents had different magic eyes... or is it just an error in my perception? ;)
I personally don’t know the answer to that 😊
Was looking at these last week (UK Ebay)and you could get 10 for £20.00 delivered (includes postage) from China, mine in my Philips is OK and have a new spare but was tempted to buy.Interesting video and you are right some of those magic eye valves are mega expensive. PS I still disagree about reforming filter caps, there old there old.:):)
That’s an incredible price! I’ll look for them myself.
As for the caps ... let’s agree to (sort of) disagree :)
@@electronicsoldandnew Well here's the link and unless I am missing something it does seem a good deal.
www.ebay.co.uk/itm/10pcs-Magic-Eye-6E2-EM87-EM84-Tube-Audio-Indicator-tube-tube-AMP-DIY/283131268505?hash=item41ebf04d99:g:0k8AAOSwYxdbh~fW
@@electronicsoldandnew as for caps, i have lots of old electronic equipment and the majority still have their original electrolytics in as they were ok as is or reformed ok😉 they can last much longer than many people think but obviously its very variable, biggest problem is heat and ripple current,
plus 'blanket' cap replacement is not a magic cure all or 'futureproofing' ..
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There’s a great article in radiomuseum about reviving magic eyes by doubling the voltage. The article suggests that it is current rather than voltage that causes degradation.
www.radiomuseum.org/forum/lighting_up_dark_eye_tubes.html
A schematic Is provided for a voltage doubler, this would make a GREAT video :)
They even suggest that the voltage doubler design will increase the life of a new magic eye. You would understand their logic far better than me I’m sure, they also reduce heater voltage.
Regards
Kevin
thanks for the link. i’ll check it out.
you can get cheap 6E2 they are look similar to your magic eye.
6p1p : I’ve actually used those. A good option.
I just found another take on a magic eye replacement in the ac7zl youtube channel. This is a combination of mechanical vision and solid state control and it's just brilliant. The realisation needs some refinement but it already looks very good.
th-cam.com/video/QFTDOZz-LlE/w-d-xo.html
The website is called hpfriedrichs where the details are given.
I think the natural progression of this is some kind of round l.c.d. screen controlled by a tiny programmable controller. In most cases, a square screen is equally applicable since the magic eye usually protrudes through a round hole on the front of the radio/instrument.
wish there was some company that could open them up and rephosphor them 😉
me too
@@electronicsoldandnew they used to 'regun' crts, so should be possible to replace the phosphor screen in these, and regetter and revacuum ..? the 'white line' type phosphor seems to last longer than the 'grey' stuff as used in em34s, etc, so maybe could use this, i've even had an em34 with a 'white' phosphor coated display disk, but stupidly didnt keep it but sold it in a radio. also seen white coated em85, still have that one!
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When a magic eye tube has gone, it's gone. For the price of a new or NOS EM84 I wouldn't bother trying to turbocharge it.
If the set has an EM34/35 then I replace it with a Russian 6E5C
Yep. I've done that a few times.
♥EM84👍
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Running it 10 to 15 percent over max recommended voltage shouldn’t be a problem as the tube is aged and at the end of its life anyway. What could it hurt. Sure wish there was a 350 volt tap 🤣
Me too
@@electronicsoldandnew to much voltage is risking flashover...
Have you seen Gord Rabjohn's solid state replacements?
th-cam.com/video/T6HPaSh0j1o/w-d-xo.html
The weak point of his round magic eye (the proper magic eye) replacement is the use of a diffuser. I think that a plastic prismatic light guide with a reflective coating would work a lot better if one took the time to build one. For linear magic eyes however, neither a diffuser or any light guide are necessary and his idea is more easily amenable to this type.
Yes, I have seen that video and looked at the project. He does a great job.
@@electronicsoldandnew How does he get the diodes soldered? Does he order the boards already populated?
Also I suggested that if the diodes were arranged vertically, it would allow for tighter packing together and hence would not need a diffuser except I forgot the slight issue of the need for a cylindrical board in order to achieve that...
Have a look at his project page linked in the video. There are a lot of details there.
@@electronicsoldandnew I did but I'll visit it again. I just found out that pcbway allows one to order aluminium pcbs pre-populated.
@@electronicsoldandnew I did but I'll visit it again. I just found out that pcbway gives the option to order aluminium boards. It also allows one to order flexible boards. I wonder what these are like and whether they can withstand the heat from the diodes.
And an OLED version:
th-cam.com/video/5Y9L4SADUDg/w-d-xo.html
Kinda clickbaity thumbnail. The eye tube in the thumbnail is new not revived.
Click baiting is really not a tactic that I give any thought to. If you see the video you’ll realise that picture is an actual shot from the video. It takes long enough to make these videos without worrying about how best to bait anyone. I almost always just take a shot from my actual video and make the thumbnail.
@@electronicsoldandnew I did see the video. At the end didn't you replace the old tube with a new one and isn't that new one the one pictured in the thumbnail?
Exactly.
It's hardly reviving it.
Cassion53 ??
its trying to squeeze a bit more light out of it 😉 i dont think it can be revived, if the phosphor is worn,, low cathode emission may be able to be 'kicked' a bit by doing similar to crt 'rejuvenation',