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Old 1st Jan 2014, 6:21 pm   #21
cmjones01
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Default Re: Rejuvenating Magic eye Valves?

I have wondered if the failure mode of magic eyes is related to ion damage in non-aluminised CRTs with no ion trap magnet. That wouldn't explain why the ones with phosphor on glass last better than the ones with phosphor on metal, unless the ones with the phosphor on the glass are aluminised, or something, which I find unlikely.

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Old 1st Jan 2014, 9:54 pm   #22
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Default Re: Rejuvenating Magic eye Valves?

In my experience, magic eyes fail because the phosphor stops emitting light, not because the cathode stops emitting electrons.

You can tell that the cathode is OK by measuring the target current and comparing with a new one. The target current is generally OK, just a shame that the electrons hitting the target stop making it fluoresce.

A higher target voltage might enable arriving electrons to penetrate beneath the surface, and excite non-poisoned target phosphor - there has been some success reported with this, and I've seen it myself - but it does not make the indicator looklike new again.
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Old 1st Jan 2014, 10:56 pm   #23
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Default Re: Rejuvenating Magic eye Valves?

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Originally Posted by cmjones01 View Post
That wouldn't explain why the ones with phosphor on glass last better than the ones with phosphor on metal,
I think it does.

Magic eyes are very different to CRTs. The final anode voltage is quite low, and there is not much of a focusing assembly. Also they are quite short.

So I suggest that ions are indeed the problem, and just take the straight line path from cathode to anode. If the anode is the target then it gets damaged, but in the EM84 type the ions probably go more directly to the anode because they are moving slowly, and so mainly miss the phosphor screen.
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Old 2nd Jan 2014, 9:16 am   #24
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Default Re: Rejuvenating Magic eye Valves?

Thank you, that's a good point. I'd forgotten that the phosphor on the glass isn't going to be the anode as well!

Ion damage shuffling around the structure of the phosphor would explain why annealing could sort out the damage, too. I have a couple of very dim magic eyes for my R1155. Now I feel like putting one in the oven!

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Old 7th Jan 2015, 8:53 am   #25
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Default Re: Rejuvenating Magic eye Valves?

Yesterday, I got out my unrestored R1155 and gave it some attention. I finally got round to trying the heat treatment on its magic eye. I propped it up in the oven and gave it half an hour at 220C, then let it cool slowly with the oven fan running and the door open. The only noticeable effects on the valve were that some old varnish on the top edge of the bulb went dark brown and the base went a little bubbly and wrinkly. Tried it in the set and...little or no change at all, comparing before and after photos with the same exposure settings. At least it didn't get worse! Maybe the treatment needs longer, or a different temperature, or maybe the microwave version would work.

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Old 7th Jan 2015, 1:25 pm   #26
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Default Re: Rejuvenating Magic eye Valves?

I wonder if heating them could actually be counter-productive?

I was thinking, putting in an oven would take ages to get the target up to temperature, it being in a vacuum, supported by insulating mica, so why not get it to self-heat by switching on? 250V at a couple of mA gives 500mW dissipation on the target itself, which being fairly small is going to get hot. Then I thought, perhaps this is what helps kill the phosphor? Types with the phosphor on the inside of the glass, which therefore running cooler, last longer, as observed in earlier posts. And the little DM70, with phosphor on target BUT only 90V at a few hundred µA again seems to last very well.
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Old 7th Jan 2015, 2:58 pm   #27
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Default Re: Rejuvenating Magic eye Valves?

I wondered about how long it would take to get up to temperature, too, given that it can only really be heated by radiation.

If the hypothesis about the degradation of the target being due to ion damage is true, then heating the target using its own dissipation will indeed be counter-productive: more current presumably means more ions. The key difference with the types with the phosphor on the glass is that the phosphor is then remote from the target, so is less likely to be bombarded with slow, heavy ions.

The DM70 is directly-heated - I wonder if that makes any difference?

I would like to find a means of heating the target of a Y63 or similar by infra-red, to get it nice and hot without bombardment, and see if that makes matters better or worse!

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Old 7th Jan 2015, 4:35 pm   #28
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Default Re: Rejuvenating Magic eye Valves?

Would it be possible to heat the target using RF. I dont mean cooking in a microwave, but say, an HF tx with a coil around the target area. A valve tx would be best I think as the mis match will be large. But some power may be transferred to the target and heat it.
Probably erronous thoughts.

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Old 7th Jan 2015, 5:06 pm   #29
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Default Re: Rejuvenating Magic eye Valves?

RF heating sounds like a good idea. They used it to fire the getter during manufacture, so why not use it to heat the target?

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Old 7th Jan 2015, 5:34 pm   #30
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Default Re: Rejuvenating Magic eye Valves?

Has anyone tried making new magic eye tuning indicators ? This would need glass working facilities, basic metal working equipment, and a high vacuum pumping plant.
Not a job for the average home workshop, but several people have manufactured valves by hand, and a magic eye looks no more complex than a triode.

https://www.youtube.com/watch?v=EzyXMEpq4qw

Valve manufacture by hand showing the equipment needed.
It might be easier to break apart the envelope of a dead magic eye, recoat with phosphor, and seal into a new envelope.
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Old 7th Jan 2015, 8:51 pm   #31
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Default Re: Rejuvenating Magic eye Valves?

Quote:
Originally Posted by Malcolm G6ANZ View Post
Would it be possible to heat the target using RF. I don't mean cooking in a microwave
Who has a duff magic eye and a friendly car garage? What needed is an induction heater, mechanics use them for flameless heating of stuck suspension nuts and other fasteners. Just an idea.
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Old 8th Jan 2015, 7:20 am   #32
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Default Re: Rejuvenating Magic eye Valves?

We have an induction hob in the kitchen... and a few duff Y63s. I will try it sometime.
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Old 8th Jan 2015, 7:47 am   #33
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Default Re: Rejuvenating Magic eye Valves?

That would be really neat, if a common-or-garden kitchen induction hob could be used! The mechanic's induction heater sounds like an ideal tool, too, though harder to find. It seems that induction heating drivers are available at fairly affordable prices on eBay, so there might be some mileage in experimenting with one of those, too.

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Old 8th Jan 2015, 9:40 am   #34
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Default Re: Rejuvenating Magic eye Valves?

The note I have seen on heat restoration of phosphors did say that overheating was very damaging so that temperature control was critical.

Note that you need a pyro-thermometer to measure the temperature of a thing in a vacuum and you need to calibrate it somehow for the material in question.
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Old 8th Jan 2015, 5:47 pm   #35
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Default Re: Rejuvenating Magic eye Valves?

I wonder if an infra-red lamp (or the sun if we get a summer) could be focused onto the target with a suitable lens in order to heat it.

It might be difficult to get a uniform temperature gradient, but a target mock up could be made and used as a trial with visible light to assess coverage. There would be no problems with convection cooling inside the valve.

We've got a really helpful dentist on the Forum - any opticians out there?

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Old 8th Jan 2015, 6:11 pm   #36
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Default Re: Rejuvenating Magic eye Valves?

Farmers also have fairly beefy IR lamps [typically 1Kw or so) for keeping freshly-hatched chooks/orphan-lambs/sickly piglets warm.

I wonder to what extent the domed glass viewing-window of a traditional end-view magic eye would act as a lens?
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Old 8th Jan 2015, 6:16 pm   #37
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Default Re: Rejuvenating Magic eye Valves?

I would think a halogen lamp would heat up a magic eye anode quite well.
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Old 9th Jan 2015, 9:58 pm   #38
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Default Re: Rejuvenating Magic eye Valves?

Quote:
Originally Posted by broadgage View Post
Has anyone tried making new magic eye tuning indicators ? This would need glass working facilities, basic metal working equipment, and a high vacuum pumping plant.
Not a job for the average home workshop, but several people have manufactured valves by hand, and a magic eye looks no more complex than a triode.

Valve manufacture by hand showing the equipment needed.
It might be easier to break apart the envelope of a dead magic eye, recoat with phosphor, and seal into a new envelope.
Both ideas have crossed my mind frequently, and I have already gathered some of the equipment and materials needed and plan to gather other materials and equipment over the course of the next year or years as I come across it. I don't yet have a suitable workshop to put them in either. One of the materials I still need to source are getters (If anyone knows a cheap source?). I already have phosphor (in powder form) and cathodes (though not of the right type). Equipment isn't yet complete either. I own a medium vacuum Edwards pump, a heating element for annealing a single valve or light bulb that I need to build an oven around, some gas burners, a spot welder. A high vacuum pump may be needed, an induction heater and some glass working equipment such as a lathe.
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Old 11th Jan 2015, 8:45 am   #39
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Default Re: Rejuvenating Magic eye Valves?

The older type do use a short life phosphor. The DM160 indicator and DM70/71 is phosphor on metal but about as long life as a modern VFD (which is similar technology to DM70 but in a planar package and still made). There are three types available as cheap NOS from China / ex USSR countries which can replace many:
Octal
Noval angel wing
Noval bar
I've used all three. The socket needs rewired or an adaptor fitted. If supply is 4V then you can use a Schottky Diode bridge ( 4 x 1N5819 or similar) and capacitor to get just over 5V, which is great but should work.

Some useful articles
Life http://www.radiomuseum.org/forum/lif...magic_eye.html
Overview and the three Russian / Chinese types http://www.radiomuseum.org/forum/mag..._patterns.html
More on the three cheap NOS types
http://www.radiomuseum.org/forum/magic_eye.html
Details on replacing EM34
http://www.radiomuseum.org/forum/rep..._the_6e5c.html
The various 6 pin and 8 pin side connect can be replaced too with a suitable adaptor.
EM80
http://www.radiomuseum.org/forum/how...4_or_em85.html

Article on ageing and rejuvenation. Increasing Anode voltage and decreasing current helps, except the indicator part grid is usually tied to cathode internally, so the only way to decrease current is to thermal emission limit by reducing heater.
http://www.radiomuseum.org/forum/lig...eye_tubes.html


I have some nearly "blank" EM34, I will try regular oven for overnight. The Microwave is too hard to control. With a regular oven the heat can only travel on the pins. A contactless IR themometer and infrared lamp or grill might be a good solution.
I've had an EM84 / EM87 type with a short that develops when it heats up. Otherwise the Noval ones are much longer life as are DM70 and DM71
http://www.radiomuseum.org/forum/dm70_operation.html

(I wrote some of the articles, so apologies if I made errors)
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