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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Jan 2008, 4:23 pm   #1
Roy
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Default Magic eye life

Is there any merit in attempting to preserve the life of a new magic eye by deliberately reducing the brightness?

A NOS magic eye is often excessively bright, a green beacon shining across the room, but as we all know, this initial brightness is short-lived.

I haven't tried this myself, but it occurred to me that it might be wise to forgo some of this initial brightness, if it could be shown that this slowed down the deterioration of the target.

Presumably, reduction of the target voltage would achieve this, but would that affect the deflection behaviour?

Has anyone tried this? With the escalating price of NOS devices, it might be worth considering.

Roy
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Old 2nd Jan 2008, 6:30 pm   #2
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Default Re: Magic eye life

I have a Soundmirror tape recorder from 1952 which is still on its original EM34.

The HT is switched off, when set to 'Play' - it is only active on 'Record'. I guess this has helped prolong its life. The wear-out mechanism appears to be poisoning of the phosphor material so it doesn't emit light, as opposed to declining cathode emission.

I'm guessing that reducing the HT would alter the deflection sensitivity, but try it! Otherwise, is it possible to add a timer with push-button which connects the HT via a relay, for a short time (say 2 minutes) when a button is pressed? It means add-on circuitry and a hole for a button - but if the cabinet is a bit ropey then you may not mind.
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Old 2nd Jan 2008, 6:43 pm   #3
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Default Re: Magic eye life

There's been discussion about this here before. I think Darius (Oldeurope) was one of the contributors.

N,
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Old 2nd Jan 2008, 6:51 pm   #4
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Default Re: Magic eye life

Quote:
Originally Posted by Nickthedentist View Post
There's been discussion about this here before.
Just spent a while looking for it, and it seems to have gone

Hope someone can prove me wrong.
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Old 2nd Jan 2008, 8:39 pm   #5
Roy
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Default Re: Magic eye life

I also did a quick search before posting, but nothing relevant came up. I doubt if the idea is original - mine seldom are!

I didn't really have any particular set in mind, I was just curious to find out if anyone else had tried it, and Howard's recent post about the Grundig set and the price of EM34s reminded me to ask the question.

Somewhere I have a NOS EM81 which is so bright it almost hurts to look at it. I'll do some experiments with the HT and see how low it can go without affecting the sensitivity.

Roy
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Old 2nd Jan 2008, 9:11 pm   #6
mickjjo
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Default Re: Magic eye life

There is an old thread here with some useful information:-

https://www.vintage-radio.net/forum/...highlight=em34

I think if I were planning to run an EM34 equipped set on a daily basis, I would be tempted to fit a small switch discretely on the back to disable the eye when nobody is looking at it. .

Regards, Mick.
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Old 3rd Jan 2008, 12:26 am   #7
ianj
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Default Re: Magic eye life

Ive fitted many of my sets over the last 8-9 years or so with russian magic eye em34 types,, and they are lovely and bright! I hate using a set with a dull eye.........I bought a russian rated 6m1, and a 6m2 for Murphy sets which are on daily, and both eyes are good and very bright still, after many years.
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Old 3rd Jan 2008, 12:50 am   #8
Michael Maurice
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Default Re: Magic eye life

My dream would be to design and build two monoblock bi valve power amplifiers.

By Bi, I mean splitting the bass and treble within the amplifiers for direct connection to the tweeters/woofers.

I'd love to have a magic eye just sitting there as a power on indicator. Much nicer and kinder to the eyes than a blue LED.
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Old 3rd Jan 2008, 1:28 pm   #9
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Default Re: Magic eye life

How about this as a magic eye substitute in the sets you use every day ...

http://www005.upp.so-net.ne.jp/y_kondo/MAGICEYE2.HTM
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Old 3rd Jan 2008, 2:02 pm   #10
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Default Re: Magic eye life

Quote:
Originally Posted by Michael Maurice View Post

I'd love to have a magic eye just sitting there as a power on indicator. Much nicer and kinder to the eyes than a blue LED.
Surely it wouldn't have to just sit there- it could wink in sympathy with the output level!

Maybe its life wouldn't be too long, but it could certainly be set up to indicate the onset of clipping, to enable maximum utilisation of any limited watts....

Chris
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Old 3rd Jan 2008, 2:04 pm   #11
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Default Re: Magic eye life

Can anyone suggest what the half-life of a magic eye is?
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Old 3rd Jan 2008, 4:46 pm   #12
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Default Re: Magic eye life

I remember the thread on MEs Darius contributed to. He'd built an RF heater and tried to heat up the cathode of a dim ME and draw off the metal contaminants, but I don't think it was a success. I think the thread was about rebuilding them in the same way that TV tubes were regunned, and the conclusion was that it wasn't a problem with low cathode emission, it was to do with contamination and all together, it was a tall order.

Here's a site discussing MEs and attempted rejuvenation.

http://home.pacbell.net/philbert/tuning_eye/tun_eye.htm

From what I understand, the EM34 type MEs dim through metal from the cathode being deposited on the fluorescent surface and either interfering with the fluorescence, or blocking the light. This doesn't seem to be so much of a problem with MEs where the phosphor is deposited on glass and light is emitted from the otherside to the electron beam, but maybe it's down to using a different phosphor.

Lowering the HT would lessen the energy of the electrons and the brightness, I'm not sure whether it would lessen the metallic contamination from the cathode, but I can see no harm in experimenting. A way of extending the life of a dim ME is to feed it with HT at a slightly higher voltage from the reservoir cap.

I can see that if EM34 type MEs were either deliberately made with cathodes designed to have low metal emission, or variability in materials used for cathodes caused some batches or brands to have low metal emission, that would explain why some MEs seem to last a lot longer than others.

Pete.
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