Please click your language flag. Bitte Sprachflagge klicken.

Unknown Optical tube

Jacob Roschy Martin Renz Ernst Erb Bernhard Nagel Eilert Menke 
Please click the blue info button to read more about this page.
Forum » Valves / tubes - Semiconductors » VALVES/TUBES / SEMICONDUCTORS in RADIOMUSEUM » Unknown Optical tube
Joe Sousa
Joe Sousa
USA  Articles: 664
Schem.: 214
Pict.: 434
06.May.09 07:02

Count of Thanks: 6
Reply  |  You aren't logged in. (Guest)   1

Gentlemen, can anyone identify the purpose of this tube?

A part number and maker would be nice too.

The face of the tube looks like an optical surface. What seems like a filament measures about 0.4 Ohms.

The tube has a structure somewhat similar to a Farnsworth image dissector.

This structure could be used to focus or track a point of light in front of the tube.

This exotic optical mystery came tube from The Fairradio part number is XTUBE-98. If you enter this part number in the search box at Fairradio, you will find the tube for sale for US$20

More pictures attached.




Ernst Erb
Ernst Erb
CH  Articles: 5711
Schem.: 13756
Pict.: 31079
06.May.09 13:50

Count of Thanks: 6
Reply  |  You aren't logged in. (Guest)   2

Dear Joe
I asked a good tube collector and member and he has answered the following to me:

It is some form of photo/imaging tube.
The end window would be probably a caesium coating and the electrode structure a scanning system.

The nearest that I know is 
this Valve site -  with some good pictures.

It would seem to have a very similar construction, but the exact structure and purpose is not known to us.

I hope we will find out one day. I have entered your tube as Xtube-98 so that you can load up your pictures. I will also move your thread to that tube page. I don't know if the base is correct I have chosen.

Dietmar Rudolph † 6.1.22
Dietmar Rudolph † 6.1.22
D  Articles: 2492
Schem.: 965
Pict.: 491
07.May.09 11:29

Count of Thanks: 6
Reply  |  You aren't logged in. (Guest)   3

As Joe mentioned, the tube indeed has some resemblance to the outline of an early Farnsworth Image Dissector. A description of the Farnsworth Image Dissector was found in

  • Zworkin, V.K.; Morton, G.A.: Television, The Electronics of Image Transmission, Wiley, 1940, pp 230 - 233 and in
  • Kerkhof, F.; Werner, Ir.W.: Fernsehen, Einführung in die Physikalischen und Technischen Grundlagen der Fernsehtechnik unter weitgehender Berücksichtigung der Schaltungen, N.V. Philips' Gloelampenfabrieken – Eindhoven, 1951

8.7. Dissector Tube.

Another and quite different type ofelectronic scanning was developed by Philo T. Farnsworth. [P.T. Farnsworth, „Television by Electron Image Scanning,“ J. Franklin Inst., Vol. 218, pp. 411 – 444, October, 1934] The principle of this pickup device is shown in Fig. 8.15.

The optical image is projected onto the photocathode, from which are released electrons whose density is distributed in accordance with the distribution of light intensity. Thus, an electron image is formed. These electrons are accelerated by a potential difference between the photocathode and the shield at the other end of the tube (or suitable metallic coatings on the wall, etc.) and move toward the shield. A magnetic field produced by a long coil focuses the electron image on the shield. This shield is perforated in the center by a tiny aperture behind which is an electrode which collects the electrons passing through the aperture. Two pairs of coils, perpendicular to the axis of the focusing fieldand to each other, deflect the image as a whole, either vertically or horizontally. By supplying one pair with a sawtooth current at line frequency, and the other with a similar current wave at frame frequency, the entire image is moved in such a way that the aperture sweeps out a scanning pattern relative to the image itself.

In other words, moving the image across the scanning aperture is exactly equivalent to moving the aperture over the image. The current to the collecting electrode has an instantaneous value equal to the photoemission from the picture element resting on the aperture, and therefore varies as the aperture scans the image, to give the video signal.


Just as in the previous pickup arrangement proposed by Campbell Swinton, the signal current has an instantaneous value equal to. the photocurrent from a single element.

The electron optics involved in this device, which goes under the name of Dissector Tube, isof no little interest. The problem is one of imaging the emission from an extended photocathode. However, it is, not identical with that of the image tube mentioned in Chapter 4, because in the latter all image points must be simultaneously in focus, whereas in the Dissector Tube only those points in the immediate vicinity of the scanning aperture need be accurately sharp. This makes it possible to use suitable components of the deflecting voltage or current to correct for any curvature of the image field when necessary. These components may be supplied either to the magnetic lens or to the accelerating voltage.


The Dissector Tube used with a conventional amplifier and coupling system, such as was described for the first mentioned electronic pickup tube, would yield a signal to noise ratio too low to produce a picture of high entertainment value, except under exceptional lighting conditions, or in conjunction with a moving picture projector. However, this type of tube lends itself readily to the use of a secondary emission amplifier. As first used in this type of tube the multiplier took the form shown in Fig. 8.16. Instead of the shield shown in Fig. 8.15, a narrow hollow metal tube contains the aperture which scans the image. This permits using an opaque photoemitter instead of the semi transparent or screen cathode, the light being only slightly obstructed by the metal tube. Inside the tube, directly behind the aperture, is a small secondary emitting element T which is made a few volts negative with respect to the tube itself. Electrons entering the aperture strike this element, producing secondary electrons which are collected by the walls of the metal tube. The net current resulting from the difference between the secondary emission current and the entering electron stream is the signal current. With a good emitter for the target T, the current will be eight or more times the incoming photocurrent. Further secondary emission multiplication was obtained in later tubes by incorporating a minute dynamic secondaryemission multiplier in the tube containing the aperture. The present form of this tube uses a multi stage static multiplier. A tube of this type is shown in Figs. 8.17 and 8.18. In practice these tubes are found to give an excellent television image when the illumination is adequate. Because of the fairly high incident illumination needed, they are rather better suited for film reproduction than direct pickup, although they are in no way excluded from practical use in the latter field.

Electronic scanning in the viewing tube, as successfully demonstrated by Boris Rosing in 1907 and in the pickup tube as proposed by Campbell Swinton in 1908, were the first two steps leading up to the modern electronic high definition system. The third important step was the introduction of the storage principle.
Zworkin, V.K.; Morton, G.A.: Television, The Electronics of Image Transmission, Wiley, 1940, pp 230 - 233

Now the 2nd text (in German)


3.1 Der Farnsworth'sche Bildzerleger

Dieses Instrument besteht aus einer sogenannten Photokathode, d.i. ein plattenförmiger, lichtempfindlicher Leiter, auf den die Szene optisch projiziert wird; s. Fig. 3.1 1.

Die optische Abbildung erzeugt eine Photo Emission von Elektronen, die eine räumliche, der von Punkt zu Punkt jeweiligen Beleuchtungsstärke der Abbildungen proportionale Verteilung besitzen. Mittels eines elektrischen Feldes zwischen Kathode und Anode wird das emittierte Elektronenbild von der Kathode zur Platte fortbewegt und mit Hilfe eines axialen Magnetfeldes fokussiert. Dies magnetisch fokussierte Bild erreicht einen Elektronen Vervielfacher, der eine kleine Öffnung besitzt. Wenn nun irgend ein Elektron diese Öffnung passiert, trifft es auf eine Oberfläche mit einem hohen Sekundär Emissionskoeffizienten, wodurch für jedes Elektron 5 bis 10 Elektronen ausgelöst werden. Diese schießen wieder auf eine darauf folgende Oberfläche, wobei dieselbe Vervielfachung stattfindet. Das wiederholt sich einige Male, bis schließlich eine vieltausendfache Verstärkung erreicht ist.

Das Merkwürdige bei diesem Bildzerleger ist der Umstand, daß die eigentliche Zerlegung durch die kleine Öffnung im Elektronen Vervielfacher erfolgt. Sie kommt dadurch zustande, daß man das ganze Elektronenbild mit Hilfe von Ablenkspulen in zwei zu einander senkrechten Richtungen ablenkt, so daß jedesmal ein anderes Bildelement vor der Öffnung im Elektronen Vervielfacher erscheint. Dieser Farnworth'sche Bildzerleger zeigt also den Vorteil, eine praktisch trägheitslose Bildzerlegung zustande zu bringen, aber er besitzt noch denselben Mangel, wie die optischen Zerleger, nämlich die unwirtschaftliche Verwendung der Szenenbeleuchtung.

Die jeweilig aktiv mitwirkenden Elektronen sind ausschließlich diejenigen, welche vom abgetasteten Bildelement herrühren; alle anderen gehen verloren.

Das Signal Rausch Verhältnis ist infolge der relativ großen, statischeu Schwankungen bei dieser geringen Anzahl Elektronen schlecht. Die Röhre ist daher nur bei hoher Beleuchtungsstärke gut zu gebrauchen, z.B. für Filmübertragungen. Bei genügend hoher Beleuchtung kann man hiermit außergewöhnlich gute, kontrastreiche und detaillierte Bilder, erzielen.

Kerkhof, F.; Werner, Ir.W.: Fernsehen, Einführung in die Physikalischen und Technischen Grundlagen der Fernsehtechnik unter weitgehender Berücksichtigung der Schaltungen, N.V. Philips' Gloelampenfabrieken – Eindhoven, 1951



This article was edited 07.May.09 11:33 by Dietmar Rudolph † 6.1.22 .

Joe Sousa
Joe Sousa
USA  Articles: 664
Schem.: 214
Pict.: 434
08.May.09 05:56

Count of Thanks: 3
Reply  |  You aren't logged in. (Guest)   4

Thank you very much for the Dissector material. It includes references about high resolution and contrast performance that I had not seen before.


The following is my google-assisted translation of the German language text you posted above, please let me know if I missunderstood the original meaning.

This instrument consists of a so-called photo cathode i. e. a photo-senstivive plate, on which the scene is optically projected, see Figure 3.1 1 [above, in this thread]

The optical image creates a photoemission of electrons, with a distribution of electrons that is proportional to the respective illuminance in the image. Using an electric field between cathode and anode, the electron image emitted from the cathode moves toward the plate with help in focusing from an axial magnetic. This magnetically focused electron image reaches a multiplier, which has a small opening. When any one electron enters the opening, it strikes a surface with a high secondary emission coefficient, where each striking electron triggers the secondary emssion of 5-10 electrons. These secondary electrons strike again on a subsequent surface, where with the same multiplication occurs. This is repeated several times until finally upwards of a thousand-fold amplification is achieved.

The dissection of the picture is done at the small opening in the electron multiplier. It is thus established that the entire electron image is dissected with the help of deflection coils in two directions perpendicular to each other, so that each time a different picture element appears before the opening in the electron multiplier. Farnworth's Image Dissector shows the advantage of virtually unblemished image decomposition, but it still has the same deficiency as the optical scanning disk dissection, namely the inefficient use of the scene lighting.

At any moment in the Image Dissection, the only captured active electrons are solely those of the dissected (sampled) picture element; and all others are lost.

The poor signal noise ratio is due to the relatively large fluctuations in the statistics in this small number of electrons. The tube is therefore only good to use at high illuminance, i.e. for film transfers. With sufficiently high illumination the Image Dissector can capture exceptional, high-contrast, detailed images.

Kerkhof, F., Werner, Ir.W.: Television, Introduction to the Physical and Technical Principles of television technology taking full account of the circuits, NV Philips' Gloelampenfabrieken - Eindhoven, 1951




Dietmar Rudolph † 6.1.22
Dietmar Rudolph † 6.1.22
D  Articles: 2492
Schem.: 965
Pict.: 491
26.Apr.10 20:21

Count of Thanks: 5
Reply  |  You aren't logged in. (Guest)   5

In "Mayers, M.A.; Chipp, R.D.: Closed Circuit Television System Planning, Rider, 1957, pp. 150 -152" a brief description of the image dissector is given, which is used in a Diamond Power Spectralty TV camera.


The image dissector is a pickup tube of the non-storage type, too insensitive to have found much application in broadcasting, but which has nevertheless been widely used for industrial television.

Figure 3-17 is an outline of the image dissector used in the Diamond Power Specialty Corp. camera.

Figure 3-18 is a photograph of this tube. The scene to be televised is focused on a translucent photocathode, the rear surface of which emits electrons in proportion to the light intensity at each point. The electron image is accelerated toward the anode by a series of ring electrodes and is focused by means of an external focus coil. The complete electron image arrives at a small fixed scanning aperture of sufficient size to pass only those electrons emitted from a small element of the photocathode.

Scanning is accomplished by moving the entire electron image horizontally and vertically, by means of the external deflection coils. As the electron image moves past the aperture, electrons representing the light intensity of each picture element at a specific instant, pass through the aperture, strike a dynode, and generate a signal current that is amplified several million times in an 11-stage electron multiplier. Note that only the electrons emitted during a small portion of the picture-time are collected and used, thus the term non-storage; also, that both the resolution and sensitivity of the tube are controlled by the size of the scanning aperture. Increasing the aperture will permit more electrons to be collected, thus increasing the sensitivity, and will at the same time increase the size of resolvable picture elements (decrease the resolution).

This latter effect is the same as that obtained by increasing the spot-size (defocusing) in the scanning beam of a picture tube. In one industrial version of the image dissector, known as the Utilicon, the aperture is a .030-inch square hole, which represents a resolution of approximately 300 lines.

Some facts of interest to the user are:

(a) Resolution capability: as noted above, ap proximately 300 lines.

(b) Required illumination: approximately 300 foot-candles of scene illumination for a good picture, using an f/1.4 lens. Lower light values have produced usable pictures.

(e) Spectral response: two types of photocathodes are available, as shown in Fig. 3.19. Both include the visible portion of the spectrum, but one peaks in the infrared region; the other in the ultraviolet region.


(d) Scanned image: 2.5-inch diagonal, requiring larger lenses than are used for 35 mm or 16 mm applications.

(e) Environment: this tube is rugged in construction and the camera using it will operate between -180C (00F) and 660C (1500F).

(f) Power supply requirements: a single – 2,300-volt supply, with appropriate voltage dividing networks, will supply the tube itself. A normal B+ supply feeds the external coils.

(g) Life: this tube has inherent long life, one reason being that there is no heated cathode required to generate electrons for a scanning beam. The Utilicon is guaranteed for one year; reportedly some tubes have been in service for as many as 10.

(h) Cost: $600.