Cathode Ray 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.

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Dumont 3ABP2
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.

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Futaba TL-3508XA 'Jumbotron' Display
Itron 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.

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Itron 2F89068 Mark III FMCRT
IEE BA-0000-P31
 

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 3000 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 3000 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.

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IEE BA-0000-P31 NIMO Tube
Telefunken XM1000
 
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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
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.

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Raytheon CK1414 Symbolray
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.

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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
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.

National Union  122P11

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