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 Post subject: magic eye tubes
PostPosted: May Sat 11, 2019 3:42 pm 
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Just wonder: is there any way to "rejuvenate" old dim magic eye tubes (6E6, 6U5) ?


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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 3:57 pm 
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Not that I'm personally aware of. If such a trick did exist, NOS eye tubes wouldn't be in such demand and command such high prices. It's the phosphorus coating on the eye shell that wears out after so much mileage.

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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 5:00 pm 
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https://www.antiqueradios.com/chrs/journal/eyetube.html

Frank


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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 5:03 pm 
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I have read articles where folks have doubled the target voltage , possibly up to 300-400V to brighten the tube. I have not tried this myself. But I found this article:
https://www.radiomuseum.org/forum/lighting_up_dark_eye_tubes.html

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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 5:08 pm 
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Your alternative.
viewtopic.php?f=12&t=335423&hilit=my+magic+eye


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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 6:28 pm 
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Location: Stafford, Texas USA
Yes you can Rejuvenating Tuning Eye Tubes below is a article from
Antique Radio Classified volume 8 February 1991 Number 8 page 16 and 17 that use a
CRT tester-rejuvenator.

Jimmie Stewart

(RESTORATION TOPICS

More on Rejuvenating Tuning Eye Tubes BY JIM FARAGO

Figure 1. The Type 6E5 tuning eye tube base diagram.
('RCA Heceiving Tube Manual," 1963, page 245.)


Upon reading Paul Bourbin's article in the August 1990 issue of A.R.C., Jim Farago responded with the following additional information
on rejuvenating tuning eye tubes. (Editor)

I read the article on "Rejuvenating Tuning Eye Tubes" by Paul Bourbin with great interest. I would like to build on Paul's article by elaborating
on which of the two eye tube elements need rejuvenating and how to build a wiring harness to connect the tuning eye tube to the CRT tube tester-rejuvenation.

Essentially, a tuning eye tube contains two triodes: one is a diminutive cathode-ray tube with a tiny fluorescent screen known as a "target" and the second, an amplifier to drive the cathode-ray tube section.

Figure 1 shows the base diagram of a Type 6E5, a typical tuning eye tube; the
cathode-ray tube section is on the right and the amplifier section is on the left.
The cathode-ray screen, or target, is labeled TA (pin 4.) The control electrode (RC, pin 2) is arranged inside the tube to cast an angular or
fan-shaped shadow on the target; the shadow varies in width according to the DC potential applied to the control element. The second triode in the tube envelope functions as an amplifier direct-coupled to the control electrode of the
cathode-ray tube section. The grid (GT, pin 3) of this
amplifier is intended to be directly connected to a receiver's diode detection circuit. (For more information, see John W. Stokes, 70 Years of Radio
Tubes and Valves, Vestal Press Ltd., 1982,Chapter 16.)

To draw rejuvenation current for brightness increase, you want to make sure that you connect to the ray control element, RC, and not to the triode grid, GT, so that current flows from the cathode surface at the "eye" of the tube. The
cathode surface controlling emission is at the face of the tube. It is very small. The RCA tube manual contains an in-depth description of tuning
eye construction and theory.


REJUVENATION PROCEDURE

Refer to the tube base diagram in Figure '1 as you proceed with the following steps:
1. Connect the CRT tester-rejuvenator heater wires, usually brown or black, to the heater pins of the eye tube (pins 1 and 6 for Types 6A85, 6N5, 6E5,6U5, 6T5.

2. Connect the CRT tester-rejuvenator cathode wire, usually yellow, to pin 5 of the eye tube.

3. Connect the CRT tester-rejuvenator control grid (grid 1) wire, usually green, to pin 2 of the eye tube (the ray control electrode.)

4. Connect the CRT tester-rejuvenator screen grid (grid 2) wire, usually red to eye tube target, pin 4.

5. Try a new, bright eye tube for emission test first to see how your tester reads
a good tube.

6. If you are using a B&K Model 300 through 440 CRT tester-rejuvenator (the most and most popular type) is being used, you should see a pattern on the "eye" (target) when testing emission.

7. Compare reading and brightness with some weak eye tubes. Use High G2 setting (on tester having G2 switch).

8. Then try the rejuvenation procedure, following directions with your tester.

Additional Testing Notes:
With B&K models, a varying voltage (O-50 v) is applied to the control grid. The emission meter monitors G2 current
(0- 1 mA is typical, at 200 volts or more).

When rejuvenating, about 600 volts is applied between grid 1 and cathode (through a limiting resistance).

HIGH VOLTAGE WARNING: Some models apply 1kV - so NO bare connections, please.
Use an enclosed "eye tube" socket from a junked radio.
Bear in mind that tube testers for radio tubes,
whether emission or mutual conductance types, do not test the target area for emission – only the triode section gets an emission test!
Mutual conductance testers, such as the popular Hickocks, test the "eye" in operation.
Emission testers do not make the "eye" glow.

My circuit information will now allow you, if you are lucky, to test and to rejuvenate the cathode surface of your eye tube where it counts - in the "eye" itself. B&K testers work as I have described.

CONVERSION HARNESS

It is best to construct your conversion harness which connects your tuning eye tube to your tube
tester-rejuvenator from a "standard" picture tube booster. lt will even have the color-coded wires
you need. (You can make one up yourself from a "duodecal" twelve-pin base from a cannabalized
CRT but, this is not advisable as the resulting harness often is not as safe to handle as one
made from a picture tube booster.) The wiring for the conversion harness using a duodecal CRT base
(10BP4, etc.) to the tuning eye tube (6E5, etc.) is as follows:

CRT Function CRT Wire Color Eye Tube
Heater 1-12 brown or black 1-6
Cathode 11 yellow 5
Grid l 2 green 2
Grid 2 10 red 4

(Jim Farago,4017 42 Ave., So., Minneapolis,MN 55406))


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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 9:07 pm 
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Joined: Mar Sun 27, 2011 5:38 pm
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Location: Acworth, GA 30101
Thank you all for your input.


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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 10:55 pm 
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So, has this worked for anyone?

Alan Douglas and I tried putting some in the MW oven for a couple of seconds to "reflash" the getter. The result was - - - broken glass. :roll:

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 Post subject: Re: magic eye tubes
PostPosted: May Sat 11, 2019 11:42 pm 
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I am going to be a doubting Scott on this one. Even CRT's that are "rejuvenated" will only last weeks to a few months at best.

If the eye tube goes dim due to emissions, then you may get a little time by "rejuvenation", but if it is dim because of the phosphor being bombarded with ions, then there is no hope. The early electrostatic CRT's, like the 7JP4 often fail due to the phosphor being destroyed by ions rather than emissions going weak. I have seen plenty that test good on my CR70 yet display a weak picture.


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 Post subject: Re: magic eye tubes
PostPosted: May Sun 12, 2019 6:58 pm 
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If this rejuvenation procedure really held such promise then you'd be seeing rejuvenated eye tubes all over the place but, as it is, not the case. It sounds like with all that setup and procedure to achieve what would be a limited amount of performance, it's still more economical and convenient to scout out for good original tubes. Even converting 1629 eye tubes to run on 6 volts filament would be more piratical.

I've always felt that NOS eye tubes tended to be brighter then necessary and methods to cut down on the brightness would also help extend the functional life of the tubes.

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 Post subject: Re: magic eye tubes
PostPosted: May Sun 12, 2019 11:59 pm 
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I suggest biting the bullet an buying a new tube. Then install a small hidden switch in the filament circuit. This way you can turn it on only when needed. I’ve done this on my daily drivers and light em up when I have company.

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 Post subject: Re: magic eye tubes
PostPosted: May Mon 13, 2019 3:29 am 
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I too have to agree that if there were a way to brighten them up again, the 6T5 shoulder tube would not cost an arm and a leg.

if we wanted to "take the edge off" when using them, is it best to decrease the target voltage or the filament voltage ?

steve

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 Post subject: Re: magic eye tubes
PostPosted: May Mon 13, 2019 5:14 am 
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Location: 253 Blanche St. Plymouth, MI USA
my tests have shown that very dim eye tubes can get up to a "usable" brightness with about a 15% filament boost. Any higher and the brighter filament blots out the green. So, maybe using an old CRT "brightener" xfmr would do (not sure how much they boosted, anyone know?).
I had a box of dud eyes I accumulated over the years... might still have them around... had about 30 dim eyes in it.
Mark Oppat


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 Post subject: Re: magic eye tubes
PostPosted: May Mon 13, 2019 10:20 pm 
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i now have only one radio that uses an eye tube after the complete downsizing over the past 10 years.

it is my beautiful crosley super 11..

https://antiqueradios.com/forums/viewtopic.php?t=229222

i have a 8-10 qty supply of used but slightly dim eye tubes. they are at probably 75% brightness with lots of life. i have these on hand to use in the radio and not feel one bit guilty about burning the tube. i play the radio a dozen hours or so a month and this used but good tube qty will most likely outlive me.

about 10 years ago, one could buy NOS 6E5 eye tubes on ebay for average of 10 bucks, sometimes less ; slightly dim-but-good ones for 5 bucks, sometimes less. 6U5 tubes were a little bit higher. i'm glad i purchased then b/c those prices are over the last time i looked.

by using the slightly dim eye tubes in the set, i can save my nice stash of NOS eye tubes for the "never will use them in my lifetime" concept :P .


steve

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 Post subject: Re: magic eye tubes
PostPosted: May Mon 13, 2019 11:25 pm 
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These tubes have a short lifetime, maybe 1000 hours, so they go bad fast and there are not a lot out there because of this. Prices reflect the short supply.


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 Post subject: Re: magic eye tubes
PostPosted: May Tue 14, 2019 12:15 pm 
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CRT rejuvenation works because the cathodes in picture tubes are subject to ionic bombardment which gradually contaminates their outer layers. The rejuvenator sets up an arc between the first grid and the cathode which burns through the contaminated layer to fresh material. This restores emission, at least for a while. The danger is that it can only be done one or two times before the cathode material is completely burned away, then you have no emission at all. What was a weak CRT ends up as a useless one.

The problem with eye tubes is generally not cathode contamination. Indeed, tests reveal that eye tubes too dim to see in room light often still have normal emission. Consequently, CRT-style rejuvenation will not help. Research indicates that the real problem is the emissive material which vaporizes from the cathodes of eye tubes. It is electrostatically attracted to the targets and poisons the phosphors. Running a higher heater voltage or a higher B+ voltage might make the tubes brighter temporarily, but it would also speed the contamination. Consequently such measures should only be applied to tubes that are too dim to use otherwise.

What seems to be the best method to prolong the lives of eye tubes is to shut the B+ off when the tubes are not needed. Certain capacitor checkers like the later Sprague TO's and the Pyramid CRA-1 do this, and there were some European radios that turned off the eye tube B+ when phono or tape input was selected.

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 Post subject: Re: magic eye tubes
PostPosted: May Tue 21, 2019 1:29 pm 
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Are Russia and China still making eye tubes? I bought 2 about 8 years ago.
Dennis


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 Post subject: Re: magic eye tubes
PostPosted: May Tue 21, 2019 1:46 pm 
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I used the Russian 6E5C in a German set.

There are MANY vendors on EBay selling these----~$10 each or less

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: magic eye tubes
PostPosted: May Tue 21, 2019 3:54 pm 
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Wonder why they never considered making an eye tube with a ion trap on the shell...

:mrgreen: :mrgreen: :mrgreen:

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