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Magic Eye Patterns

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Papers » Tubes and valves (history, technique etc.) » Magic Eye Patterns
           
Michael Watterson
 
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11.Oct.11 21:02
 
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Applications of "Magic Eyes" also known as "Tuning indicators", "Magisches Auge" and "Cat's Eyes"

The original use was in 1930s to help people tune radio sets more accurately. Now when Magic Eyes are expensive and moving coil meters are cheap, it's hard to realise that in 1930s to 1960s the valve was far cheaper! The moving coil meter was too expensive.  The Animation is of Y63 as mounted in a Greyshaw Instruments CR Bridge test meter when a leaky capacitor is connected of about 15 M Ohms. It really is mounted at right angles to the normal radio usage.

Applications

  • Tuning Indicator on Domestic and Military radio receivers.
  • Tuning Indicator and AGC amplifier
  • Peak level or Null indicator on Direction finders
  • Peak level or Null indicator on test equipment maybe even up to 1970.
  • Tape recorder audio record level
  • More complex Tuning meters for FM Radio with Stereo Indicator

About the “Magic Eye” or "Cat's Eye"

The original types are the 6E5 family in 1934, Domestic radios from 1935. This includes the 6E5, 2E5, 6G5, 6T5, 6U5, 6AB5 and 6N5. All have  similar characteristics and use the same 6-pin base, except the 2E5 has  2.5 volt heater. The 6E5 was introduced by RCA in 1935,  The 6U5G is Octal version of 6 pin 6UG, very like a Y63, Some models were made not only in 6 pin and 8 pin versions but also in straight and bulb sided glass. Some "end view" Magic eyes had side contacts instead of pins.

Bulb sided and straight sides

The "magic eye"  has an amplifying triode, which is used to increase the sensitivity of the eye. The 6E5 uses a plain triode, while the 6G5 has a variable-mu triode to let it handle larger voltage swings. The 6AB5 and 6N5 were intended for battery radios, having lower filament consumption. The rare 6T5, introduced by Arcturus and Sylvania in 1937, has an annular ring shadow around its center, rather than the conventional angle shadow. Some models have a pentode.

Often a "G" suffix means an octal version of a 6 pin type and a "T" suffice a Bulb sided version rather than straight tube. Thus a 6U5 is straight sides 6 pin and 6U5G is Octal and if a Bulb octal version exists (it would be like a Y63) it might be marked 6U5GT. But note that this is NOT a rule, the G and T suffixes can be for other reasons entirely. The 1629 was a common WWII 12.6V version of the 6E6 type.

A similar round pattern is found in the types 6AD6, 6AF6 and 6AFG. They are not at all like the 6E5 types as they have two separate areas and no internal triode. They have TWO control grids, each controlling the opening angle of its own dark wedge independently of the other. This was useful for things such as FM radios where one side might show signal strength and the other would show multipath. Here is an article on the 6AF6G explaining how to use the independent patterns.


6AF6G

The 1629 is  commonly  found in WWII military equipment. Its base is octal,and it has a 12.6 volt heater rather than the usual 6.3v heater. It has a 6E5 design, with a target plus a driver triode, and it must be connected a bit differently from the others. There may be NOS surplus 1629s still available. With AC supply a voltage doubler of two capacitors and two 1N4007 will power it from 6.3V

Another still available “Magic Eye” is the 6AL7. Its display pattern was square, not round, divided into three rectangular bar-graph indicators. Two on top, side by side, with a double-wide third bar below. 

 


6AL7 fully lit (or 6AL7GT)

Being an "end view" type the bars are really quite small. The 6G-E12A is a Japanese “Magic Eye” . It has an octal base and its eye pattern is rectangular, with two open wedges which are controlled separately. Also Japanese is the 6ME10. It looks like a 6355.

 

Noval/B9A side view "Magic Eyes.

In the  early 1950s, miniature "magic eye" tubes similar in size to B9A arrived. Most were developed by Telefunken in the first half of 1950s. The EM8x series was all 9-pin miniature. Though some manufacturers used WWII surplus end view Octal types maybe till 1959. The EM80 and EM81  have patterns in a half-oval shape with a wedge in the middle, or “Angel Wings” patterns. The EM80 (Russian 6E1P aka 6E1n aka 6BR5), 81, EM84 (6E2n aka 6E3p) or EM87 might be suitable for use in a new design. It's best to just search eBay for cheap Russian valves. The EM80, EM81 appear to be later production for many Manufacturers than the EM85 of 1952

 

The Russian 6BR5, roughly equivalent to EM80, EM81 and similar to EM85 of 1953, one of earliest Noval side view "Magic Eyes"

 

The EM84 and EM87 (6HU6) are quite common. They have two bars that grow toward each other on an much longer panel that are brighter when they overlap.

 

EM87
EM84, EM87 (Radio sets mounted vertically or horizontally)


The EAM86 are relatedto EM84s, except the bars are horizontal to the base (wrapping around the tube barrel partly), rather than vertical. This makes the bars quite small but makes the package smaller

EAM86
EAM86



The brightest are probably the EM84, EM87, 6AF6 and 6AD6. Note that most of the miniature EMxxxs are side-view, while all the pre-1950s types are viewed from the end. The 6AD6/6AF6s give bright displays but require control-electrode voltages of more than 50 volts, as they do not have internal driver triodes.


The 1952 DM70 (CV2980, 1M3) (wire ends) and DM71, (1N3, 1M1, Y25) (wire pins) are developed for valve battery radios. The filament is for 1.5 volts and HT 45v to 90v. The pattern is an glowing green exclamation mark about 3/4" high. The DM21 is older Octal 1.5V “Magic Eye”  The DM70/DM71 is probably the smallest Magic Eye ever made (the DM160 is a VFD annuniciator and not a "magic eye" at all)

 

 DM70 fully lit

Wega battery Table Radio using  DM70 as tuning indicator

Grundig portable reel to reel tape using DM71 for recording level

There is no apparent difference between a DM70 and DM71 except the DM71 has short pins for a socket and the DM70 is wire-ended.

Any of the tubes can be looked up on the tube database and Members can see which models of Radio, Tape recorder or Test instrument used them.

 

Types of Magic Eye” by Pattern

Note that tubes of same pattern and even same base may not be equivalent.

 

End view: 6 pin, similar Octal, Loctal or side pins

1: One moving shadow

2E5, 2G5, 6AB5, 6AF7A, 6E5, 6E5c, 6E5D, 6E5GT, 6E5M, 6E5S, 6G5, 6G5G, 6M1, 6ME5, 6ME10, 6N5, 6S5, 6U5, 6U5G, 12ZE8, 1629, CV51, CV504, CV843, CV1103, CV1756, CV1906, CV2747, HF3110, ME41, ME91, ME920, NR69, OSW3110, VI103, VT98, VT138, VT215, Y61, Y62, Y63, Y64, Y65, 63ME

 

2: Two moving shadows, one control

6X6, 6Z-E1, AM2, AW6, E1180, EFM1, EFM11, EM31, CV1077, V177

 

3a: Dual sensitivity, one shadow moves more.

6CD7, 6AF7, 6AF7G, 6M2, CV394, CV1434, EM34, EM4, UM34, 64ME, UM4

3b: Two moving shadows, individually controlled

6AD6, 6AF6, 6355, R2164

3c: Dual sensitivity, dual control no amplifier.

6AF6, 6AF6G (article)

 

4: One Moving, One fixed shadow

6H5

 

5: Four shadows, all in sync

4678, AM1, EM1, EM3, TV4

 

6: Four shadows, but two are more sensitive

EM5, EM11, EM35, UM11, UM35

 

7: Expanding ring. (only TI65 has visible wires)

6EG5, 6UG5G, 12UG5G, TI65

 

8: Half illuminated

6E5MT, 6ME2, EM71, HM71, UM71

 

9: Half illuminated, no overlap

EM72 (Loctal 8, B8G) No Peak, permenent shadow area, dual Triode

 

10: Expanding band

6T5

 

11: Two Rectangles with two shadows

6GE12

 

12: Rectanglar with two shadows, center square

6GE12A

 

12: Top view, three bargraphs

6AL7, 6AL7GT, CV3707

 

Side View Noval/B9A Miniature types

13: Side view, meeting vertical bars (single control)

4FG6, 4HU6, 6E2, 6E3p, 6FG6, 6HU6, 19FG6, CV5434, CV10407, EM84, EM85-E, EM87, EM840, PM84, PM87, UM84, UM87

 

14: Side view single long vertical bar

EM800

 

15: Side view meeting horiziontal bars (single control)

6GX8, EAM86

 

16: Single shadow side view "angel wings"

6DA5, 6DG7, 19DA5, 19DG7, EM81, EM85, UM81, UM85

 

17: Dual shadow side view "angel wings"

6E1p, 6BR5, 19BR5, EM80, UM80, Y119

 

18: Dual bargraph side view (Bulbus Noval B9A)

EM83, UM83

 

19: Dual Side view, meeting vertical bars (separate controls)

EMM801, EMM802(different style)

 

20: Dual Side view, meeting vertical bars, small 3rd bar/annunciator

EMM803

 

Special Miniature package

21: Growing Exclamation mark, Battery Valve Radio

DM70, ( CV2980, 1M3), DM71, (1N3, 1M1, Y25). Sometimes called "Keyhole" Indicator.

   The DM70 or DM71 at full signal.

 

Some of the EMM valves are very expensive due to demand for HiFi Stereo meters. The basic EM series though are affordable. For pre-1950s vintage sets it should be possible to use a cheaper alternative "Magic Eye" unless you wish to keep the Wireless completely original.

 

More unusual "Magic Eye" tubes

The 6E-E4 Japanese Finger tube might be a magic eye type.

 

Tubes that are NOT "Magic Eyes" but Neon (or Argon) Bargraphs or Tuning Indicators.

Aslo VFD such as DM160 or IV-15 are not Magic Eyes or Tuning Indicators but a different kind of Triode based annuciator.

 

Commonly available and cheap  Magic Eye valves (Tubes)

Also search for: Magisches Auge on eBay "worldwide"

  • Octal End View: 6E5S, 6E5G, 6G5G  
  • Noval side view "Angel wing": 6E1P, 6BR5, EM80
  • Noval side view "Angel wing": EM81
  • Bar: EM84, 6FG6, 6E3P  
  • Bar: EM87, 6E2

Don't assume NOS (New Old Stock). Some are Ex-Equipment so may be dim as "Magic Eyes" wear quickly. Some may actually be new (possible of some Russian and Chinese, but could be 1990s NOS). 

Other models are available, NOS of DM70/DM71 and 6AL7 are reasonable price. Some others are very expensive, especially the later EMMxxx as well as rare old ones.

It's a myth that Sunlight or UV destroys a "Magic Eye" in a few days. But they are less reliable than ordinary valves and the target "wears". Increased HT can help a lot to get some more life when it's dim.

"Magic Eyes" can be quite well simulated with LEDs in a plug-in module powered from Heater supply if no replacement can be obtained. Either an LM3914 (simple types) or a PIC cpu (complex patterns and variations of brightness of shadow and overlap) can be used.

This is based on an Article I originally wrote  signed "Watty" for "Tectír" the Irish Technology Magazine site.

Related Articles

 

This article was edited 19.Dec.11 22:34 by Michael Watterson .

Michael Watterson
 
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30.Jul.15 14:09

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The 1E4A-V (transliterated) is only a similar idea. Slightly lower filament voltage. Possibly put a 4.7 or 6.8 Ohm resistor in f- lead

See the tube page.

Available on ebay NOS from 1981 at reasonable price as I write.

  
rmXorg