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-   -   Rejuvenating Magic eye Valves? (https://www.vintage-radio.net/forum/showthread.php?t=102398)

don200002 31st Dec 2013 9:19 pm

Rejuvenating Magic eye Valves?
 
Can someone please tell me would it be possible to rejuvenate Magic Eye Valves in a similar way that we used to rejuvenate TV tubes????

Thanks,

Don.

Sean Williams 31st Dec 2013 9:36 pm

Re: Rejuvenating Magic eye Valves?
 
I would say not, the target actually gets stripped of it's emmissive ability, cranking the heater volts up would give a limited increase in brightness, but not for very long.

mark pirate 31st Dec 2013 10:56 pm

Re: Rejuvenating Magic eye Valves?
 
Yes, No chance I am afraid, I need 3 Y63 and a couple of TV4 and a TV6.
NOS eyes are getting very expensive, and I don't want to pay more for the valve than the set is worth!
I have avoided used valves because they probably have no emission left :(

There was a thread on LED replicas recently, so there is an alternative.
:beer:
Mark

don200002 31st Dec 2013 11:47 pm

Re: Rejuvenating Magic eye Valves?
 
Thanks for the replies, I guesed as much due to the price of replacements, I suppose the only way to improve the performance is to up the heater or target voltage but thanks for all your help,

Don.

Maarten 1st Jan 2014 3:41 am

Re: Rejuvenating Magic eye Valves?
 
As long as the problem is in the cathode rather than in the emissive layer, any valve can be rejuvenated with varying degrees of success. It never hurts to try!

Simplest test could be to let it glow at an elevated heater tension (for example 8V instead of 6,3V) for a few minutes. Then plug it back into the set and see whether there is any difference at all. If there is, some improvement should be possible. Also if the valve is operated at a higher heater tension while in the set (or in a test setup) and the eye is much brighter at 8V this shows the emissive layer still has some life left.

Phil G4SPZ 1st Jan 2014 10:27 am

Re: Rejuvenating Magic eye Valves?
 
I've read a couple of articles which suggest that the only way of getting more life out of tired eyes is to increase the target voltage, up to 500 volts. There is an article in the latest NZVR Bulletin with a suitable voltage doubler design. Coupled with reducing the heater voltage by 20% or so, a greatly extended life is claimed for both old and NOS eyes.

GMB 1st Jan 2014 11:03 am

Re: Rejuvenating Magic eye Valves?
 
I note that there has been some research done on rejuvenating electroluminescent displays which are using a very similar phosphor, and this suggests that annealing at a temperature of between 180C and 240C does significantly help (maybe takes about 2 hours, and the temperature is fairly critical - don't overdo it).

boxdoctor 1st Jan 2014 12:17 pm

Re: Rejuvenating Magic eye Valves?
 
I wonder if the loss of brightness is always entirely due to loss of emission by the cathode.
It could be that the phosphor coating on the target might be deteriorating. Targets often look discoloured in the illuminated area. In that case, it would be very difficult to ever achieve the original brightness.

turretslug 1st Jan 2014 12:36 pm

Re: Rejuvenating Magic eye Valves?
 
They do seem to go to a dull grey from the initial light appearance- yet the heat of a mA or so of HT on the metal cone/crescent must be negligible. Is there some sort of chemical combination/poisoning going on with the base metal?

It's a shame they are short-lived, I'm sure if there was a simple answer, the proverbial army of tinkerers would have found it. At least the low current requirement suits straightforward voltage doubling, heater boosting takes a bit more thought. It rings a bell that some posh sets with variable selectivity only switched eye HT on in "narrow" for tuning, removing it on "fidelity" positions. Perhaps a subtlely hidden switch for show use would eke out these increasingly scarce and pricey beasties.

I have a couple of tired EM81s around, the oven idea is tempting on the grounds that there's not much to lose! :beer:

Maarten 1st Jan 2014 1:26 pm

Re: Rejuvenating Magic eye Valves?
 
On a Dutch forum, there has been some discussion about rejuvenation using a few seconds of microwave exposure at a few hundred watts. It seemed to work sometimes and blow the heater on other occasions. Maybe GMB is on to something and there is some limited effect on the emissive phosphor layer as well.

In my earlier post, I used the words emissive layer as well, but omitted the word phosphor. I'm sorry for any confusion.

cmjones01 1st Jan 2014 1:34 pm

Re: Rejuvenating Magic eye Valves?
 
Quote:

Originally Posted by GMB (Post 651979)
I note that there has been some research done on rejuvenating electroluminescent displays which are using a very similar phosphor, and this suggests that annealing at a temperature of between 180C and 240C does significantly help (maybe takes about 2 hours, and the temperature is fairly critical - don't overdo it).

That's an interesting idea - it should be easy enough in a domestic oven. Can you point us to any of the research?

Chris

neutronic 1st Jan 2014 1:34 pm

Re: Rejuvenating Magic eye Valves?
 
I donīt feel responsible !!!
And I donīt apologize to your wive.

Some euphoric stories about putting them in the microwave!
Only for a very short moment.
Half of them are as good as new and half of them explode.

http://www.gloeidraad.nl/radioforum/index.php?id=140756
(translation by Google?)

a very Happy 2014
Jard N.

mark pirate 1st Jan 2014 2:19 pm

Re: Rejuvenating Magic eye Valves?
 
I have found the Thread on Replica magic eyes, click the link in post#1.
https://www.vintage-radio.net/forum/...ead.php?t=8123
:beer:
Mark

Herald1360 1st Jan 2014 2:56 pm

Re: Rejuvenating Magic eye Valves?
 
Quote:

Originally Posted by neutronic (Post 652030)
Half of them are as good as new and half of them explode.

Still sounds well worth a try, what's to lose- a useless magic eye?

And maybe a sweep out of the microwave before SWMBO catches you at it ;D

turretslug 1st Jan 2014 3:16 pm

Re: Rejuvenating Magic eye Valves?
 
With a shorting twist of wire across the heater pins. (Though a well-known law says that that would form a resonance.)

Phil G4SPZ 1st Jan 2014 3:35 pm

Re: Rejuvenating Magic eye Valves?
 
The Dutch report mentions 3 seconds at 900 Watts, or 2,700 Joules.

I have a very old 700 Watt microwave oven, due to be scrapped next month, and a pile of dim eyes, so I will definitely give it a try at about 4 seconds.

mark pirate 1st Jan 2014 4:03 pm

Re: Rejuvenating Magic eye Valves?
 
Please let us know how you get on Phil, I have a few that are very dim, and a couple that have no display at all!
:beer:
Mark

don200002 1st Jan 2014 4:15 pm

Re: Rejuvenating Magic eye Valves?
 
I have an EM35 with no display at all, 3 seconds at 850 watts and there is a very dim display.
P.S. I did take the precaution of putting it in a bubble wrap bag before "cooking".
Best of luck,
Don.

GMB 1st Jan 2014 4:36 pm

Re: Rejuvenating Magic eye Valves?
 
Quote:

Originally Posted by boxdoctor (Post 651998)
I wonder if the loss of brightness is always entirely due to loss of emission by the cathode.

No, it hardly ever is that.

The thing that is really interesting about magic eyes is that it is the ones with metal luminescent targets that fail badly.
The EM84 and similar last way longer.

The anode current tells you that it isn't a cathode problem.

The same type of failure occurs in the radioactive dials on old military equipment. They also used ZnS phosphor but this time activated by the radiation. They usually don't glow at all by now (but are still radioactive).

There are really only two possible ways that phosphors stop working. It is either because the "activator" is not working, or because they are contaminated by something that takes the energy away better than the ZnS. The common green ones are probably ZnS and copper and I think they work by the copper catching the energy and passing it to the ZnS to emit the light.

There is unfortunately a real possibility that the damaging mechanism is metal evaporating from the cathode and embedding in the target causing the energy to be diverted away from the emitter. This may be hard to fix although I wondered about creating a high voltage discharge with the target as cathode. The other reason, which the heat suggestion addresses, is that the copper activator diffuses into the ZnS and the structure no longer works properly - but can be restored by heat.

The microwave suggestion could work in either of these ways - but a more controlled method might give clearer results. But there is little to loose.

audiomagpie 1st Jan 2014 5:46 pm

Re: Rejuvenating Magic eye Valves?
 
Someone (and I'm sorry, I can't remember who) was selling and demonstrating LED ones at the last Golborne meeting. I was so impressed, I bought an EM34 version but haven't fitted it as yet.

Maybe someone else was there and know's who it was?

Greg


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