The thread rating is reflecting the best post rating. Have you rated this thread (best post)? | History of Tuning Indicators: meters, graphs, Magic Eye, LED |
Ernst Erb ![]()
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The history of Tuning Indicators is nearly as old as radio itself. We are not beginning with the sounders, galvanometers etc. to show a line currant and signal in telegraphy which have existed well over 100 years. We begin with the indicating tools and methods for wireless reception - not transmitters.
Separate Voltmeters and Milliamp-meters on a Ducretet "7-Tube-Piano-Type" See also Zenith Multiceiver MC-3 from 1921. Here you find an example of a Remler radio (Superhet 1924/25) with a voltmeter for battery conditions to help adjust the rheostat. This Scott Radio (1926) uses a voltmeter which can be switched for A battery (filament, Volts) or B battery. See also Mende Superhet EZ123 from 1925.
1: Signal strength meters (AVC) A: Radio Amateurs Wikipedia picture: S-Meter of a Ten-Tec Orion amateur radio transceiver. S 9 = -73 dBm. This is a level of 50 microvolts at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms. S meters for AM show an "S" 1- to 9 (with 6 decibels (dB) difference for each number) and above the decibels which exceed the 9. Example S2 = -115 dBm or 0.40 microvolts in 50 ohms on HF, S9 = receiver input power of -73 dBm = 50 microvolts in 50 ohms (VHF bands -93 dBm or 5 microvolts in 50 ohms). B: Early signal strength meters (before AVC) Galvanometers or Milliammeters (Moving Iron or Moving Coil Meters) are used.
C: AVC Automatic Volume Control Wheeler: Original application filed July 7, 1927, serial no. 203,879, and in Great Britain July 3, 1928. Divided and this application filed November 10, 1930, serial no 494,558. patented Sep. 27, 1932 as 1,879,861. "Volume Control". But see also Espenschied and Bowen (1921 Bell). Against drift Clarence W. Hansell filed Nov. 1, 1927 a patent "Automatic Tuning" for RCA, patented May 9th 1933 as no. 1,907,965. For automatic tuning, John E. Gardner of Chicago, assignor to Grigsby-Grunow, filed a patent August 23, 1926 with title "Radio Receiving System", which was published as patent 1,897,252 Fab. 14, 1933. Alan Douglas told me about it, because it covers also other issues which are of interest here, like signal-seeking. There are co-pending applications, serial number 123,528 and 129,717 mentioned, also for 1926. Harold A. Wheeler Filed Dec. 8, 1927 "Radio Volume Control" serial no. 238,488, patented July 12, 1932 as 1,866,687. At least Wheeler's later design included a milliammeter as a tuning indicator. He and others worked on such patents on AVC like: D: The first variable-mu tubes for AVC
The trick was done with variable spacing of the grid wire spiral. The differential spacing has to be done very smoothly. The second generation of variable-mu tubes had a closer grid spacing to the cathode to get a lower grid voltage requirement so that it was easy to use the direct way via a diode rectifier without the need for amplification of the bias signal. Different appereance and function for tuning indicators There were first moving pointers (meters) then at about the same time projected meter pointers, change of intensity or color for bulbs, pilot lamp or Neon as well as pattern indicators like linear neons and graphs, later Magic Eyes and solid state indicators. Here you find only some of the better known systems and methods: Used were simple meters - or in the case of some manufacturers, optically clever solutions to suit the decor of the cabinet. Lets start with a nice one:
Zenith 103 Ultra from 1932 (perhaps 1931/32) shows a Signal Strength Meter (and Push Button Tuning for 9 stations!). The detail of the meter is seen on this Zenith model 92 from 1931/32 with the writing: "Tune for greatest swing to right" You can just see the needle in the right corner for a strong station. Photo by courtesy of Mason B. Cohen.
Signal Strength Meters in Europe See a nice physical location of a meter within the scale (right) like for Philips Denmark Octode Super 626HU-17 from ca. 1935.
2: Shadow tuning meter We use this term for a "Shadow Tuning Indicator" or Shadow Indicator with a normal instrument behind a translucent screen, showing only a shadow from the needle. Below you will find the other principle with a rotating shutter or vane with a coil around it. Both use the light from a rear mounted lamp.
Shadow Indicators in Europe Left: 1933 Stassfurter Imperial 53. 3: Shadowgraph The principle: Problems: The wax on the windings melted causing the vane to stick. Sometimes a double peak was apparent due to a bent vane. 10mA meters were used initially and later 8mA models. Solutions of two big competitors: Early version Philco Shadowgraph Philco Model 15X (and 15DX) from 1932 with 4 gang variable condenser (band filter entry), a tuning indicator meter and push-pull output. Detector rectifier, triode 37, is used as a diode (anode on ground). The AVC negative voltage is fed over R40 and R28 to bias the grid of 1st IF and via R17 and coil 19 the 1st detector and through R9 the RF stage bias. There is a rectangular cutout area above the scale that allows light to pass through the disc, surrounding the control vane. Look only at the bar on top of the (moving) scale This simple solution which acts similar as a later Magic Eye in form of a bar was used by Philco on many models during 1932 through 1937/38. As Philco 200X from 1934 shows, the tuning aid could also have its own dedicated control tube (here a tube type 37). Until 1937 more than 150 models had this device. You find this Shadowgraph also on Philco Model 012 Output Meter. Zenith Shadowgraph Model 935 from 1935 = right picture above OTHER Manufacturers with Shadow indicator (Shadowgraph): Atwater Kent uses the principle for instance in models 310, 510, 711, 808A of 1933/34.
4: Dimming Pilot Lamp
5: Flash-O-Graph FADA
6: Saturable core reactors and bulbs Begins with a single pilot lamp - see for instance here - which Canadian Westinghouse model 103 represents a whole family (1933). But there are quite some sophisticated systems like: Sean Barton, USA has sent me these photos. Thanks to him we see the details of the different scales coming up by switching waves. General Electric Colorama E-91 (and E-95) were the first Coloarama models. We have included the term "Colorama" to the models with this type of tuning indicator like models E-101, E-105, E-106, E-115, E126, E-129, E-155 and the farm radios FB-72, FB-73, FB-76, FB-77. Some are simpler systems like A-205E and A-208E from later years. Synchro-Silent-Tuning (Grigsby-Grunow, brand Majestic)
Neon indicators are an electronic approach instead of either mechanical or with conventional lamps. As with the meters or lamps one could have a simple solution by using the anode current of an IF tube. Alexander Senauke, New York, signed Dec. 16, 1929 and filed Dec. 27, 1929 his patent for a Neon lamp as tuning indicator - which was patented on Jan. 5, 1932 as no. 1,839,419. In theory the first models could have AVC based Neon tuning indicators from 1930 - but I was unable to find such models. Who knows more? The simple 2 element neon lamp can be used - up to 4 element neon tubes:
There have been quite different approaches - sometimes given a brand name: Atwater Kent Motorola, FADA etc. FADA ![]() Ad above: models with KW from 1932, RA, RC and RW chassis etc. Sparton, Sparks-Withington United Kingdom Tuneon BT from GEC - right = top view
Germany 8: Magic Eye 9: Post Magic Eye My thanks go to the various members who uploaded pictures to models like Hans Amberger, Dietmar Rudolph and to Roy Johnson, UK, who gave me some pictures and helped me finding the way - especially also to improve my English wording. The "technical" pictures "Fig. 19-xx" are from Ghirardi, "Modern Radio Servicing", 1935, the "Fig. 5-18" from Ghirardi/Johnson 1951, "Receiver Circuitry and Operation" and "289 to 291" from Ardenne, "Handbuch der Funktechnik und Ihrer Grenzgebiete", Vol. 2, 1935. See also Joe Sousa
This article was edited 10.Mar.11 10:19 by Ernst Erb . |
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Ernst Erb ![]()
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Gradually you will find here some additional examples of tuning indicators which where used before (and sometimes also after) the arrival of the Magic Eye.
Scale of the Ingelen Geographic US26W from 1935. This picture from Alois Steiner shows a nice scale in the shape of a map of Europe. At that time not only the Neon indicator showed a station but also one of the more than 100 light directors made from solid glass showed the physical location on the map. Unfortunately a few years later the Geographic Scales from Austria were not functioning correctly due to the change of frequencies for many braodcasting stations ... The sets are now a very interesting collector item. Very interesting is that the idea t show a station on a map has come many years before - but the solution was quite a different one - to achieve something similar. I was not able though to find a model - but a patent only - filed March 24, 1931 by Glenn W. Carpenter for General Electric as "Geographic Station Indicator", patented Dec. 22, 1931 as 1,837,948. See the solution below. This article was edited 10.Aug.09 08:14 by Ernst Erb . |
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Roy Johnson Schem.: 21 Pict.: 132 12.Aug.09 00:51 Count of Thanks: 92 |
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The attached 3 pages from Wireless World of August 10th 1934 outline the principle indicators then available and gives practical advice on their operation and application. |
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Ernst Erb ![]()
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I just added some Atwater Kent models with a "shadow tuning indicator" which is often called a Shadowgraph - also in connection with Atwater Kent. I don't know if Shadowgraph was a brand name or if it is just a general word for such indicators. Today for not so differentiated collectors it is just this - but I would like to know it the correct way. Any solid information on that? |
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Michael Watterson
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Broadcasting to the public starts in the earliest 1920s and at first if Radio sets have a tuning indicator at all it is a milliamp meter. Then we have all kinds for strange and wonderful ideas for Tuning indicators in the mid 1920s and especially from 1930 to 1935 until the "Magic eye" or "Cat's Eye" (invented in 1934) is established as illustrated by Ernst Erb above such as the Neon Tuneon and some complex Shadowgraphs and lamp arangements as well as simpler ideas. Sandor Selyem-Tóth has suggested some additional examples
Simplified Time lines for Magic Eyes
Here linked is overview of types of Magic Eyes and patterns. What happens after Magic Eyes?
After the Magic Eyes and Russian Neon Bargraphs we only have the mechanical meter as Analogue display device on a Radio of Tuning or Signal. All the Bargraph types are "on/off" technology. Two factors led to the cessation of the wonderful glowing "Magic Eye", or "Cat's Eye" in Radio sets by the end of the 1960s:
1970s to 1980sHere are some typical models of meter in my collection removed from scrap sets of the era.
These Meters are all to approximately the same scale. 1990s to 2011Originally when Amateur and Professional radio got Digital readout (Nixie then LED) for frequency the driving was by discrete logic or a frequency counter IC. In later 1980s when Microprocessor controlled the synthesiser and PLL and display cheap enough for domestic radio the signal level or tuning was still an analogue meter or a separate IC driving an LED bargraph as the cheap consumer processors didn't generally have an internal analogue to digital converter. By the late 1990s it was possible for the microprocessor to "read" the AGC line and operate a simulated meter or bargraph integrated into the same LCD (portable, car or mains) or VFD (Car or mains) panel that also displays frequency, memory channel, reception mode(s) and any other desired information. The LCD won't displace the VFD as the VFD takes actually less power if you need bright backlight, and the VFD being a triode valve works at temperature extremes that destroy or freeze the liquid in an LCD cell. The VFD is also oddly more robust and very much less degraded by UV light with time. But for compact battery portable applications the LCD is supreme, and when no backlight is needed surpassing OLED. The early 60s is really the end of Magic Eyes in the last AM/FM valve radios and the last tape-recorders to use them. There are three methods used to drive bargraphs from the Radio Signal for tuning
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This article was edited 02.Dec.11 21:55 by Michael Watterson .
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Emilio Ciardiello ![]()
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In addition to the many tuning indicators listed in the comprehensive overview given by Ernst, I would also remember two more families used in the past. |
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In its article "Tuning Indicators, A Review of the Various Visual Tuning Devices Available and Some Suggestions as to Their Use" of August 10th, 1934, "Wireless World" brings the reasons for and some of the used systems. Roy Johnson has loaded this article up after I wrote abut the same subject. Most people think that the Magic Eye of Allen Balcom Du Mont was the first idea to use a miniature cathode-ray-oscillograph. But there were several patents before. One in particular, the Micromesh Tunograph, was an interesting solution and is described in that article. Fortunately the article as such was written before Du Mont filed his patent - and proofs that other solutions were at hand.
Standard Telephones and Cables (STC) realized this Cathode-ray Indicator. It functions by causing a green spot on the fluorescent screen to vibrate at the frequency of the received carrier wave. This creates a green line on the fluorescent screen and the length of the line can be made to vary with the strength of the incoming signals. The light is caused by the strikes of the stream of electrons on the fluorescent screen. The stream is emitted from a hot cathode, fouused and moved laterally by deflecting plates like in an ordinary CRT tube - but having only one pair of deflecting plates.
H. W. Parker filed Aug. 16, 1932 a patent for "Tuning Indicator For Radioreceivers" and received in March, 13, 1934 a patent 1,951,036 for the following device:
H. M. Wagner also filed his "Tuning Indicator Tube" in June 27, 1935 and received the patent already Aug. 18, 1936 number 2,051,189. That causes believe that he was the first if one looks only to the patent number or date.
Also the patent of T. J. Scofield for a "Gas Discharge Tuninbg Indicator" he filed Jan. 25, 1935 was patented earlier, June 14, 1938 as 2,120,955 (a new Viso-Glo), than Du Mont's.
There have been many patents before the Magic Eye for tuning indicators based on the CRT tube but we can clearly give the credit to Allen Balcom Du Mont for the Magic Eye which came on the market 1935. The 6E5 was registered by RCA on June 27, 1935 and used by RCA in consoles in 1935.
Allen B. Du Mont was working on "Cathode-Ray" tubes for television but we call the Magic Eyes "Electron-Ray" tubes for distinction. All are CRTs.
This is in short what I found here: "After Du Mont was an engineer for Westinghouse he became chief engineer for the De Forest Radio Company in Passaic, NJ. Presumably he worked in private since he sold the patent to the RCA in 1932. The De Forest company went into receivership in 1933 and RCA took the assets. Du Mont used his money for pioneering early oscilloscopes, television sets and TV broadcasting and prospered greatly during WW2 with defence electronics." But I did not find a patent for the Magic Eye before the one you find a picture of here below, filed Sept. 18, 1934. Still, that article is full of interesting information.
Who was Du Mont?
Allen Balcom Du Mont was born Jan. 29, 1901 in Brooklyn NY, died Nov. 15, 1965 New York NY. He joined the Westinghouse Lamp Company, Bloomfield, N.J., in 1924 as an engineer in the development laboratory. There he developed high-speed manufacturing and testing equipment for vacuum tubes. Encyclopaedia Britannica: "In 1928 Du Mont became chief engineer of the De Forest Radio Company, Passaic, N.J., where he became interested in the patents and equipment of Charles F. Jenkins, who had established an experimental television station in the early 1920s. Working from Jenkins’ patents, Du Mont set up a simultaneous picture and sound broadcast in 1930 and concluded that electromechanical systems were inadequate for practical television and that a purely electronic system was needed.
Du Mont set up a company in 1931 that later was known as Allen B. Du Mont Laboratories, Inc. He improved cathode-ray tubes and developed the modern oscilloscope, widely used in the laboratory for the measurement and study of wave forms.
In 1937 Du Mont began manufacturing the first commercial television receivers, which were based upon his improved cathode-ray tube. His company also established experimental television transmission facilities and marketed the first postwar television receivers."
His work for Magic Eyes is not mentioned.
What did Du Mont patent?
Du Mont received 419 patents, some dealing with Cathode Ray Tubes like 2,087,280; 2,098,231; 2,162,009, 2,163,256 (filed Sep. 18, 1934 see picture); 2,186,635; 2,225,099; 2,269,115 etc.
His first patent was:
Aug. 21, 1925 serial no. 51,561 for "Mount for Radiotubes", patented July 9, 1929 as 1,719,968. Third patent: Feb. 4, 1926 serial no. 86,077 a "Sound operated Circuit controller", patented Feb. 9, 1932 as 1,844,117: "...Provides a means whereby a radio set may be rendered operative or inoperative from a remote point by the creation of a given sound, as by the proper impact or clapping of the hands, thus making it possible, if desirable, to terminate the broadcasting while seated at a distant point. ..."
For tubes followed: Nov. 1928 serial no. 321,846 for improvements in radio tubes, patented Feb. 21, 1933 as 1,898,351. Or: Filed Oct. 7, 1932 "Cathode ray instrument for measuring electrical quantities", patented May 29, 1934 as 1,960,333.
The first patent for the Magic Eye:
Allen B. Du Mont, Upper Montclair, NJ, assignor to Allen B. Du Mont Laboratories Inc. filed Sept. 18, 1934 Serial no. 744,498, patented June 20, 1939 as 2,163,256.
Part of the patent text: "A cathode ray tube having beam producing means comprising a concentrating cylinder, an insulating cylinder having two holes there-through, a spacer connecting said insulating cylinder with said concentrating cylinder, a tungsten wire filament threaded through the holes in said insulating cylinder, a molybdenum wire secured to said tungsten filament, and an ocyde coating on the tip of said molybdenum wire. 2nd: A cathode ray tube having a fluorescent screen, means for producing a plurality of beams comrising a plurality of concentrating cylinders ..."
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Greetings fellow enthusiasts, and thank you for your excellent threads regarding tuning indicators. This topic is very near and dear to me.
I have much respect for Allen B. DuMont. He was an intelligent inventor and a major contributor to the development of television, but I don't give him exclusive credit for the invention of the magic eye tube. I believe that both DuMont and Herbert M. Wagner should share the credit for this invention. My rationale is as follows:
I give DuMont full credit for the novel idea of using a cathode ray tube for a tuning indicator. In his patent filed May 28th of 1932 entitled "CATHODE RAY DEVICE", he states starting at line 22: "It is contemplated that the invention will find wide use in connection with the indication of the tuned or resonant condition of radio receiving sets...". In the diagram in this patent, he also shows his tube as being controlled by the AVC voltage of the receiver. The device he designed, however, did not have the appearance of the magic eye tube that we are used to seeing, and was nothing more than an oscilloscope tube with a single axis. An illuminated spot would move in one direction or the other depending upon the voltage applied.
Nevertheless, RCA needed a license for this patent in order to use any cathode ray device as a tuning indicator. I'm not sure what year it was, but RCA president David Sarnoff purchased the rights from Allen DuMont. Between May of 1934 to June of 1935, various engineers working for RCA filed patents for at least five various cathode ray tuning indicator designs. One particular design by Herbert M. Wagner illustrated in patent 2051189 became the magic eye tube that we have come to know and love. Wagner's design was and still is attractive. In 1935, it was innovative, inexpensive, and very much marketable as cutting edge technology.
The origin of the term "Magic Eye" is another reason I do not give DuMont full credit for this device. I have been unable to find exactly when the phrase was first used, however, no tuning indicator was documented as a magic eye tube until after the 6E5 was introduced. The earliest document I have found using the term Magic Eye is the 1936 RCA advertising brochure where it is enthusiastically and extensively used.
Though currently have no proof (documentation), I believe that the design by Herbert M. Wagner (which resembles an anotomic eye) provoked the term magic eye.
I have intentions of some day visiting the Soda House at the Hagley Museum to look through the archives of the David Sarnoff Library to find out if information exists regarding these developments.
With Best Regards,
Howard
This article was edited 10.Jun.12 18:43 by Ernst Erb .
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Our member Roberto Guidorzi is restoring a Magnadyne Radio model SV13, made in Italy (Torino).
He saw this article and has sent to me some very nice pictures and his toxt to publish here. Thank you, Roberto, I would not be able to write that nicely and precise:
"The design of the Lesa shadow tuning indicator is very simple but also very effective from a mechanical point of view (no springs, no currents in moving circuits).
Looking at the picture in attach we see that it contains a cylindrical magnetic circuit with an air gap surrounded by a fixed magnet (that can be rotated by means of an external small lever). Inside the cylinder we find the optical shutter constituted by a magnetic metal flapper connected to the cylinder by two pivots. No springs at all; the (very stable) equilibrium position of the flapper is determined only by the magnetic field inside the cylinder and by rotating the magnet around the cylinder we can change the inclination of the shutter to change, if desired, its rest position to compensate the zero-signal current through the coil.
The lower part of the magnetic cylinder is surrounded by a fixed coil with a resistance of approximately 2940 ohms that is inserted in the plate circuit of the I.F. amplifier tube. This field generated by this coil acts in an unsymmetrical way on the flapper so that the deflection of the flapper is modified by the current through the coil. Of course the flapper/shutter is inserted on the light path generated by a small lamp and its deflection modifies the length of a shadow on the front of the indicator."
The main picture for the explanations:
Here you have the looks of it. You might find more pictures on the model page (link) when Roberto has done his surely good restoration, trying to keep everything most original, at least original looking.
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