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Radios with Tuning or Magic Eye Tubes
Radios with Tuning or Magic Eye Tubes
A feature that caught the buyer's eye was a tuning meter to make it easier to tune in stations. Electromechanical panels meters were available but were expensive and usually required tedious panel cutout patterns. In those days a tube was a lot cheaper and I think "cooler". These tuning tubes would open up or cast a shadow based on how strong a station was. The Magic Eye Tube was the invention of Allen Dumont in the 1930's who later sold it to RCA. Dumont was a manufacturer of cathode ray tubes and oscilloscopes at that time.These tubes were made to provide different patterns based on what the radio maker thought was best. These tubes glowed green because of the phosphorescent material on the "target" area (part you see).
Either a 6U5 or 6E5 Tube Shown
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Mission Bell 410 (1939) Los Angeles, CA. Using 6AF6G Eye Tube. Used 1st generation true AA5 tubes. 12A7GT, 12K7GT, 12Q7GT, 35L6GT and 35Z4GT.
6AF6G Tuning Eye Pattern (Untuned Indication). Stationized lighted dial.
The 1st generation AA5 tubes had grid cap connections.The 35Z4GT has no pilot lamp tap.
BELOW: Notice the push button tuning mechanism. To set the station one has to turn each knob to make sure the tuning capacitor will adjust to your selection.
Packard Bell 46G (1940) Los Angeles, CA Tansformer operated, using 6AF6G Eye Tube and 6SA7, 6SK7, 6SQ7, 41 and 80 tubes.
Stationized dial light and 6AF6G Tuning Eye Pattern (Untuned Indication)
AM and SW set. This set has upper band and lower band oscillillator station alignment.
Roomy chassis underneath.
RCA T80 (1938) Camden, NJ Transformer operated using 6U5 or 6G5 Eye Tube and 6SA7, 6SK7, 6SQ7, 6SF5, 2- 6F6G and 5Y3G tubes. Push pull amplifier produces 5 watts of audio. Has connection for phono or TV connection.
Closer Look at 6E5 (6U5 is rare). Tuning Eye Pattern LEFT (Untuned Indication). Shadow is at the bottom (Hard to see). Has a very informative panel:
Top view of chassis. Notice on the left, a pair of 6F6G tubes in push-pull amp configuration with a 6SF5 metal tube (far right) as a phase inverter. Notice the blank spot on the tuning capacitor (right section). Probably a provision for adding an RF amp stage.
Roomy chassis underneath. With all the extra room left over they could have added a tuned RF amp stage for better sensitivity especially for SW band.
Mission Bell 389AW / 3810 (1938) Los Angeles, CA. Transformer operated 3 band radio using rare 6T5 Eye Tube along with 6A7, 2-76, 6K7, 6F5, 42 and 80 tubes. Has nice Art Deco style cabinet.
6T5 Tuning Eye untuned display. "Bullseye" style tunning. Circular pattern, as the station is tuned in the shadow circle gets smaller.
8 tubes used. Two 76 type tubes used (shield tubes next to each other). One as a detector the other as the SW oscillator. IF freq is 465 KHz, right before the standard 455 KHz was used.
Total Restoration- Paper capacitors restuffed with modern smaller capacitors.Three generations of resistors used, dogbone, early molded and smaller carbon composition types. Mixed generation of tubes using prong types and octal based glass and metal along with older number designation versus newer standard numbering tube types. A lot going on under the chassis for a 1938 set.
SHOWCASE
SHOWCASE
Getting more brightness out of a magic eye tube
The Mission Bell 410 shown above is a transformerless radio using a magic eye tube 6AF6G. The maximum plate voltage provided to the 6AF6G is about 105 Volts. The minimum voltage is specified at around 90 Volts and the maximum is 250 Volts. In order to get a viewable magic eye one has to put the most sensitive one in. That's what Mission Bell probably did. 6AF6G magic eyes were inexpensive then, so Mission Bell could hand pick the "hot" magic eye tubes. That doesn't work in vintage radio restore as these tubes are no longer made. I needed to get a higher plate voltage to accommodate variations. In parallel with the 35Z4GT rectifier I added a solid state 1N4004 and a 4.7 uF electrolytic. The 1N4004 is more efficient than the 35Z4GT, producing a higher voltage output. While the tube rectifier produces about 105 Volts, the solid state diode produces about 125 Volts. Result a noticeable increase in brightness. Adding an extra 1N4004 and 4.7 uF electrolytic connected in a voltage doubler configuration can get it even brighter. The risk involves shortening the life of the magic eye phosphor coated target. One may have to lower the output voltage a little to get the best balance of life versus brightness.
A Rare Magic Eye: The 6T5 "Bullseye Pattern" Tube
I believe that this is the only commercially made magic eye tube with the circular style shadow. As shown on the first photo, an untuned station provides the largest circular shadow. As the signal strength of the station gets stronger the circlular shadow shrinks looking like a "bullseye". People are willing to pay a lot of money to get a working 6T5.
1N4004 diode and 4.7 uf electrolytic providing independent and higher plate voltage for the 6AF6G magic eye tube.
TOP PHOTO: Untuned
BOTTOM PHOTO: Tuned
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