Detection & Imaging Tubes

Photomultipliers and photocells are light-detecting tubes used in electric eyes, video cameras and various astronomical applications. Photocells are simple gas-filled devices consisting of a photocathode and anode, while photomultipliers, or PMT's are more complex high-vacuum devices. PMT's are extremely sensitive, some capable of detecting single photons. They amplify their photocathode's extremely small signal by passing the discharge through a chain of specialized electrodes called dynodes, which are each held at a successively higher voltage potential. In 9-stage PMT's, the voltage difference between photocathode and anode are typically in the range of 1000V, though they can be operated at lower voltages with a corresponding decrease in signal amplification. The sensitivity of a PMT is expressed in the form of quantum efficiency, a percentage describing the ratio between the number of incoming photons versus the number of electrons produced by the photocathode.

 


Hamamatsu R1250
 

The R1250, with a length of 10 inches and a diameter of 130mm, is a monster of a photomultiplier. This tube, designed for use in scintillation counters, is a 14 stage device with a peak spectral response of 420nm. The tube uses a large 20 pin base; sockets are undoubtedly hard to find.

Hamamatsu R1250
EMI 9826B
 

The EMI 9826B is a small end view photomultipler tube designed for use in the scintillation counters used within positron emission (PET) medical scanners. The 9826B pas a peak wavelength of 420 nanometers and is characterized as having a high speed response and immunity to magnetic fields within a relatively compact package. The unusual base is designed to facilitate testing; even though the tube is a flying lead type, it's long gold leads have been welded to a 14 pin button base. This is so the customer can insert the tube into a test fixture for characterization prior to installation in a final device, at which point the button base would be clipped off.

EMI 9826B
Honeywell 113228
 

This long narrow device is a special type of phototube, designed to detect UV light. Unlike most phototubes which have an argon fill, this tube is filled with neon. The 113228 is used exclusively in Honeywell Purple Peeper and Mini Peeper industrial flame sensors. It can be difficult to find sockets for the small three-pin base.

Honeywell 113228
RCA 1P21
 

The 1P21 is a side-viewing photomultiplier designed for extremely low light applications. The tube has a lime glass envelope, a humidity-stable beige base, and outputs maximum amplification at 380 nanometers. This tube is capable of detecting single photons, and will be destroyed if powered up while exposed to ambient light.

RCA 1P21
RCA 1P40
 

The 1P40 is a fairly standard example of a cold cathode phototube. The tube contains a centrally located anode and a curved photosensitive cathode, most likely coated with cesium to act as a getter. The tube is lightly pressurized with an argon fill gas to enhance conditions inside the tube. The 1P40 is sensitive to red and infrared light - an S1 spectral response.

RCA 1P40
GM Labs #2 'Visitron'
 

'Visitron' is yet another brand name concocted by the tube companies to take a boring argon filled phototube and make it sound new and exciting to the consumer. Despite the goofy name, the tube itself is actually quite attractive, with a large curved envelope and a four-pin phenolic base. The tube's serial number is 304,279.

GM Labs #2 'Visitron'
RCA 1P41
 

The 1P41 is an end-viewing miniature phototube with a three pin base. The tube has a spectral response S-1 and an argon fill gas. According to RCA, this tube is intended for relay applications.

A scan of the RCA Photosensitive Devices and Cathode Ray Tubes catalog, which contains specifications on this tube, can be found at World Power Systems.

RCA 1P41
Teltron 1149 Orthicon
 

An Orthicon tube is a large camera image sensor that saw widespread use in television broadcast cameras from the 1940's to 1980s. Orthicon tubes incorporate a transparent photosensitive plate that is scanned from behind by an electron gun; this allows all the components of the tube to be arranged linearly, a significant advantage over the unwieldy Iconoscope tubes they were designed to replace. Iconoscope camera tubes had an opaque photocathode material that required the scanning electron gun to be placed in front of the point where light entered the tube. This example, an 1149 tube made by Teltron, is fairly representative of the construction style used in Orthicon tubes. Though Teltron is best known nowadays for their physics and educational tubes, they were prolific producers of camera imaging tubes during the Cold War.

Teltron 1149 Orthicon
RCA 7038
 

A vidicon tube is a sort of 'reverse CRT'. Instead of sweeping a beam of electrons across a phosphor coating to display a picture, vidicon tubes sweep an electron beam across a photosensitive target to generate an image from the light striking the target. The 7038 is a fairly standard vidicon tube, with a length of 5.6 inches and a diameter of 1.1 inches. Vidicon tubes are still used today in some security cameras.

RCA 7038
RCA 921
 

The 921 is a side-viewing phototube with an argon fill gas. The tube has an unusual form factor, with two metal caps sealed to a glass tube. Each cap acts as one pin for the device. As with the 1P41, this tube is intended for relay applications.

A scan of the RCA Photosensitive Devices and Cathode Ray Tubes catalog, which contains specifications on this tube, can be found at World Power Systems.

RCA 921
Varian 0981-82850-301
 

The Varian 0981-82850-301 is a thoria iridium ion source for use in Varian gas detectors. The device is barely a vacuum tube, as it has no glass envelope; the envelope for the tube remains attached to the gas detector. To protect the ion source from a world of dirty humans, the device is shipped in a protective plastic cylinder, which contains stern warnings to handle the device by its base only.

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Varian 0981-82850-301
RCA 931A
 

The 931A is a side viewing, nine-stage photomultiplier, an improved version of the original 931. Tubes of this type do not produce an image; instead they are designed to measure and amplify very weak sources of light. This tube was manufactured with both a black and tan bases. The tan base is made of a special material that is more resistant to humidity, and as such is more desirable than the black base variant.

RCA 931A
RCA 991
 

The 991 is primarily used as a voltage regulator, but has also been known to be used as a phototube in some situations. Unlike most phototubes which use argon as their fill gas, the 991 has a neon fill. The 991 can also double as a neon indicator.

RCA 991
Raytheon A704
 

With an envelope size of just over an inch, the A704 is one of the smallest phototubes ever made. This tiny two pin tube does not even have any discrete internal components, the photocathode is just a chemical, most likely a lead sulfide photoconductor, painted onto the back wall of the envelope. The tube has an argon fill gas.

Raytheon A704
Cetron CE-36
 

Here is another miniature phototube with a three pin base. The CE-36 is a side view tube with an argon fill gas. According to the book Tube Lore, this is a spectral response S-1 tube commonly used in projectors.

Cetron CE-36
Hamamatsu R488
 

The R488 is an end-view phototube designed to be particularly sensitive to UV light. Unlike many other phototubes, which have an argon fill gas, the R488 is a hard vacuum tube.

Hamamatsu R488
Valvo 90AG
 

A British made argon filled phototube in a standard seven pin envelope. This tube has particularly good print quality on its part number and logo; it is not quite up to the standard set by Western Electric tubes, but is far better than the typical "dissolves when looked at" print used on most tubes.

Valvo 90AG

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