Cathode Ray Tubes


Futaba TL-3508XA Jumbotron Display

Back in the time before LEDs, large outdoor displays like the 'Jumbotrons' seen in many stadiums had to rely on tube technology for their displays. The Futaba TL-3508XA flood beam CRT shown here is a rare example of this quite unusual technology. The flood beam CRT differs from a normal CRT in that the electron gun within does not produce a focused controllable beam. Instead, electrons are sprayed in a wide cone across the entire front of the phosphor screen, effectively turning an image display device into a simple light bulb. The TL-3508XA actually contains multiple flood beam devices in a single envelope, enough to display eight pixels of RGB data. A control grid sits in front of each electron gun, allowing the intensity of each pixel to be varied by a low voltage control signal. Thousands of tubes such as this are required to build an entire Jumbotron display.

Tubes were assembled into modules like the Sony A-6279-869-A, which had quick-connect fittings for easy removal. Tubes such as this only had an operational lifespan of around 8000 hours, a means to quickly replace and remove dead display elements was mandatory. The A-6279-869-A modules are equipped with plastic shade bars to increase the contrast of the display.


Futaba TL-3508XA Jumbotron Display
Itron HB 2F89068 Mark III FMCRT

The Itron 2F89068 is a flat matrix cathode ray tube, or FMCRT for short, which was used in 'Junbotron' style large scale video displays. FMCRT cells display images using a series of flood beam CRT electron guns with overlapping X and Y gate electrodes, effectively converting a typical cathode ray tube into a single pixel bitmapped device. The example shown here is a Mark III FMCRT, which differs from earlier FMCRT displays in that it contains a contrast-enhancing magnifier that improves outdoor visibility while allowing for a smaller pixel size. Each tube contains four separate pixels which each contain four individually controllable subpixels. Since the human eye is most sensitive to light in the green band of the electromagnetic spectrum, each pixel contains two green elements in a typical RGGB configuration to enhance the apparent brightness of the display at long distances. Each subpixel can display up to 256 different brightness levels, allowing for millions of possible color combinations. Despite it's smaller size, this display has a longer lifespan than the Futaba device shown above, and is rated for 12,000 hours of use at normal operating voltages.

Mark III FMCRT's were manufactured with three different part prefixes; HB, HG and HR, which each had different pixel dimensions and power requirements. The example shown here is an 'HB' version.


Itron HB 2F89068 Mark III FMCRT
Soviet ILD3 Series

The ILD3 series is a family of Soviet flood beam cathode ray tubes intended for the construction of 'Jumbotron' style large video displays. Each CRT is designed to represent only a single pixel, and lacks the deflection and focusing components necessary to form a controllable beam. A single modulator electrode allows the diameter of the electron stream to be controlled, but in normal operation cathode rays are vomited out in a conical spray that covers the entire front of the tube. Each color is assigned a separate part number, with the ILD3-S producing a blue output, the ILD3-K producing red, and the ILD3-L having green phosphor. At first glance it seems like astounding overkill to design and manufacture a cathode ray tube that has been 'crippled' down into a glorified light bulb, but such a device does have distinct advantages. A flood beam CRT such as the ILD3-K can be turned on and off at a high speed with a relatively low voltage, a near necessity when displaying full motion video. Additionally, a traditional incandescent light bulb produces a copious amount of heat, and consumes substantial current to produce that heat. A typical Jumbotron-style display would need many thousands such bulbs to display a usable image, and could quickly become too hot to handle. Given the alternatives, flood beam CRTs were literally a decision of cold hard logic.

It should be noted that even though the thumbnail image shows these displays arranged in a 3 tube RGB configuration, originally the tubes would have been mounted in a four tube RGGB cluster. Human eyes are most sensitive to green light, and doubling the number of green elements in each pixel was a trick used by both Russian and Japanese manufacturers to improve the brightness of their early large scale 'Jumbotron' displays.


Soviet ILD3 Series Cathode Ray Tubes (ILD3-S, ILD3-K, ILD3-L)
IEE BA-0000-P31 NIMO

IEE's rare foray into the world of cathode ray tubes, the 'Nimo' display is a very special variant of the common cathode ray tube. A Nimo tube contains an array of 10 electron guns, each with a digit shaping mask, which are aimed at the center of a phosphor screen. Activating a particular gun will cause the given digit to appear on the surface of the screen. Number's displayed on a Nimo tube are crisp and much more visually appealing than other display tubes, but the phosphor coating on the face of the tube can easily become burned-in after prolonged use. Worse, Nimo tubes require a 1700 volt anode supply as well as a 1 volt power supply for the filament, which makes them much more difficult to work with than other display tubes. The 1700 volt supply connects to an anode stud that exits the side of the tube envelope, a special socket was supplied by IEE to make this difficult connection.


IEE BA-0000-P31 NIMO Tube Display
Telefunken XM1000

Telefunken's XM1000 cathode ray numeric indicator was the European competitor to the IEE's Nimo devices, which are covered above. The XM1000 is smaller than a standard single digit Nimo tube, but is contained within an oval envelope that allows for tighter side-by-side installation of multiple tubes. The XM1000 contains twelve electron guns that are projected through shaped masks to display numbers on a phosphor screen, which allows for the display of numbers as well as left and right decimal points. As with the IEE devices, the XM1000 requires an anode voltage of several thousand volts to function, this is delivered through a clip connection on the side of the envelope.

Telefunken XM1000 Cathode Ray Tube
EMI Tabby CV147 & CV148

The CV147 and CV148 are part of a series of tubes produced by EMI for use in World War II era night vision systems. Each tube contains a phosphor coated screen that is sensitive to IR light, which is mounted in a tubular envelope with flat glass faces. These tubes require approximately 3000 volts to function; WWII era night vision scopes used a non-replaceable Zamboni pile to generate the high voltage needed. The high tension would be applied to the metal rings on each side of the tube, with the flat windows on each end of the tube sandwiched between a stack of conventional optics to produce a complete image. After the war many of these image converter tubes were sold off as surplus to the electronic hobbyist community, which is likely how the two tubes shown here entered the private sector.

The CV147 and CV148 are part of a larger family of tubes produced by EMI, ranging from part numbers CV142 to CV149, which were all produced on the same production line. After manufacture each tube would be tested and binned for maximum voltage, at which point a corresponding part number would be assigned.


EMI Tabby CV147 & CV148 Image Converter Tubes
Dumont 3ABP2

The 3ABP2 is a two-gun electrostatic deflection CRT, capable of projecting two beams at once. The tube's 3-inch screen is coated with a high persistence green phosphor. Though the separate guns share a common heater, each gun has it's own set of deflection plates and can be independently positioned. This feature makes it a favorite for homebrew electronics projects, as each beam can be dedicated to drawing a different portion of the screen.


Dumont 3ABP2 Two Gun Cathode Ray Tube
Raytheon CK1414 Symbolray

Raytheon's CK1414 'Symbolray' tube is a special type of monoscope designed for generating characters for data processing systems. The CK1414 works much like a vidicon tube, but instead of a light-sensitive screen, the CK1414 has a fixed metal plate which contains stencils of letters and numbers. In operation, an electron beam is swept in a raster pattern wide enough to cover a single symbol on the target plate. Electrons reflected off of the target are collected by a ring shaped collector around the perimeter of the tube. When the beam intersects a character, the flow of electrons to the collector is reduced, lowering the brightness of an attached display device's electron beam, which is being swept in the same raster pattern as the beam striking the target plate. In this way characters can be recalled at will and used to draw text and information on command. The target plate in the CK1414 contains 64 characters, which include capital letters and numbers as well as mathematical symbols and various cursor characters.


Raytheon CK1414 Symbolray Cathode Ray Tube
Educational Hickok Cathode Ray Tube Kit

This unusual device is a glass kit, manufactured during the 1960s and 1970s, that allows the user to construct a Huggins-style cathode ray deflection tube. The kit includes metal parts that can be crimped together into a deflection plate and anode assembly, filaments, a glass envelope, a glass button base, and assembly instructions.The resultant tube has two long metal plates mounted 90 degrees to each other, which can be used for electrostatic deflection. The instructions avoid the complexity of fusing the base and envelope together by having the user seal the seam with silicone sealant or JB Weld, this allows the base and envelope to be reclaimed afterwords and used to build other tubes. The imperfect vacuum allows the electron beam to be seen, which is the only 'display' this tube provides... there is no phosphor coating on the front screen of the tube. It should be said that this project is not for the feint of heart... the builder would need a 100 volt power supply and a 40 micron vacuum pump to assemble and use this tube, as well as enough common sense to not be electrocuted or poked full of holes by exploding glass.

The example shown here was actually obtained as surplus from a middle school science department. It is amusing to picture a time when public education was so metal that 13-year olds were building their own cathode ray tubes as an educational exercise.


Educational Hickok Cathode Ray Tube Kit
RCA 913

The RCA 913 is an electrostatic deflection CRT with a tiny one inch screen. This octal base tube has a curved spherical screen and an unusual metal shell, instead of the glass neck seen in most CRT's. The 913 was specifically targeted at the hobbyist and experimenter market, and had a selling price of $4.00 in 1936.

RCA 913 Cathode Ray Tube
National Union 122P11

One of the smallest CRTs we have ever seen, the 122P11 has a screen diameter of only 0.75 inches. This diminutive display makes use of a normal 9 pin miniature base, allowing the tube to be used with commonly available sockets. The 122P11 uses electrostatic deflection, and as such does not require an external deflection coil to function.

National Union  122P11 Cathode Ray Tube (NU 122 P 11)

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