Magic eye tube

Magic Eye is the colloquial name for a Abstimmanzeigeröhre, a special electron tube, which indicates the strength of a signal on the principle of bar graph display as light bars or sector and is often installed in older radios, but also in televisions.

Also, tape recorders, audio amplifiers and other equipment had magic eyes as a level indicator.

In stocked with electron tubes receivers from the mid-20th century to the 1970s shows the " Magic Eye " and the later emergence of "Magic Band" to exactly how the device is set to the transmit frequency of the receiving station. The display tube assumes the function of a tuning indicator, for which usually the control voltage of the receiver is used directly. The reason for this display is that such phase-locked loops for automatically adjusting, balancing and ongoing readjustment of the receiving frequency were indeed available for its time receivers such as radios control devices, but these impacting here with an enormous amount of components, which the receivers more expensive so that only luxury units had this feature.

Forms and applications

We distinguish between different shapes, the magical subjects, the magic tape and the magical balance. The original magic eyes had a round fluorescent screen (hence the "eye "); However, the operating principle is always the same, only the method of presentation is different.

When tape recorders (usually tape or subjects) has been set, the modulation of the recording based on the deflection of such a display tube. In older amplifiers ( eg so-called orchestra amplifiers ) you could see through such advertisements and determine overdriving the signal height. Today this VU meter ( Drehspulmesswerke ) or LED bar graphs are used.

Is (eg bar-shaped display = magic tape ), a transmitter set bad or the signal is low, the non-luminous region between the bright beams on the entire width is extended. The cleaner the reception or the higher the signal, the narrower is the dark area between the beams and disappears in a strong station or reaching the clipping altogether. With excessive overlap the bright areas of both sides, leading to a double strip light intensity, which serves as a highly visible alarm signal to turn down the level accordingly.

Semi-circular "eyes" ( = magical subjects, such as EM80, EM81 or EM85 ) show reception is poor, a fan-out, with better only the center is illuminated.

Complete round displays are so-called real magic eyes: they showed cross-shaped four sectors of a circle, whose angle changes (eg EM35 ). For weak driving an X is similar to a St. Andrew's cross visible under full control of a broad cross or almost a full circle. Here there are variants (eg, EM11, EM34 ), which have two light angle different sensitivity. This allows the receiver to the lighting angle more sensitive to weak stations to vote properly, while can be matched with the less sensitive to strong light angle transmitter, while the sensitive part here already entirely controls appears. This has been done with different steepness of the per variable light angle integrated Verstärkertrioden Tech.

There are round magical eyes, in which only two circular sector-shaped luminous surfaces are present, the angle increases at full load (eg EM34 ), as well as versions with only one angle (eg 6E5 ).

• Various Magic Eye

The illuminated compartments of a EM80

The "magic tape " a EM84 (often installed horizontally )

A couple EM84 in operation, left in full ausgesteuertem state

Operation

Abstimmanzeigeröhren are electron tubes, the electron current is directed onto a fluorescent layer, usually made of pure zinc orthosilicate ( willemite ), or a mixture of willemite and zinc oxide. This always lit in green or blue-green light and was applied to the correspondingly shaped anode or inside the glass bulb.

In newer designs, the luminous layer is no longer applied to a metallic support tube in the inside, but directly on the inner glass surface of the envelope. The light-emitting layer was not formed from pure zinc orthosilicate, but from willemite with an addition of zinc oxide. Pure Willemite loses by electron bombardment relatively quickly luminosity, while the zinc oxide wins even in brilliance by this treatment. Here, this phosphor mixture shows a blue-green cathodoluminescence emitted a deep green while pure willemite here.

The direction of deflection is done with control electrodes ( ridges ) that create or even just push apart ( voiding eg magic tapes) emanating from the cathode electron current into bundles.

Thus, the electrons can flow better from the crystalline, non-conductive light emitting layer, a graphite layer ( Aquadag ) has often been the luminescent layer still applied. In tubes with the luminescent layer on the transparent conductive oxide layers of glass are used.

However, there were also tuning displays based on special glow lamps in which a control electrode as in a bar graph, the cathode cover could be changed.

Examples

The best-known types of the E-series ( the E is 6.3 V heating voltage ):

• Eye: EM 4, 11, 34, 35
• Subjects: EM 71, 80, 85
• Band: EM 84, 87, EMM 801, 803

The type EM 83/84/87/800 ( magic tape ), and the EM 80 ( subjects) are still available as new parts, the type EM 34/35, however, are very rare and therefore expensive.

Many types of the corresponding U-design ( series heater 100 mA) are still available, for example, the UM 80/81 / 84 The UM earlier frequently used 11 on the other hand has become quite rare.