REX (ZANUSSI) MOD. RB24 CHASSIS BS212.4 INTERNAL VIEW.

 

 

 

 

 

 

 

 

The ZANUSSI CHASSIS BS212.4 is the last chassis for B/W television sets using tubes mixed with semiconductors.

tubes used:

- PL84
- PY88
- PL504
- PCL805
- PCF200

Thermionic tubes, also known as vacuum tubes or electron tubes, are electronic devices that were widely used in the early 20th century as amplifiers, oscillators, and rectifiers in electronic circuits. These devices are made of a sealed glass envelope that contains a vacuum, and they rely on the flow of electrons from a heated cathode to a positively charged anode to produce a current. The cathode is typically made of a material that has a low work function, such as tungsten or thoriated tungsten, and is heated by a filament to emit electrons through a process called thermionic emission. The anode, on the other hand, is usually made of a metal that can withstand high temperatures and is shaped to form a series of plates or grids that control the flow of electrons.

Vacuum tubes have always been used to control the flow of electricity through electronic components.

These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.

Of course, there must be a hard vacuum (about one millionth of normal air pressure at sea level) inside the bulb (modern light bulbs often contain gas), otherwise gas molecules would block the movement of electrons. To preserve this hard vacuum, after a thermionic valve has had all the air pumped out of it, a "getter" made of reactive metal such as barium is fired by means of an electrical discharge and/or RF induction heating through the glass wall, which creates a silvery coating on the inside of the glass that will absorb any remaining gas molecules, including ones that can be released from the valve materials.

Classification
One classification of thermionic vacuum tubes is by the number of active electrodes. A device with two active elements is a diode, usually used for rectification. Devices with three elements are triodes used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have multiple additional functions made possible by the additional controllable electrodes.
Other classifications are:

•  by frequency range (audio, radio, VHF, UHF, microwave)
•  by power rating (small-signal, audio power, high-power radio transmitting)
•  by cathode/filament type (indirectly heated, directly heated) and warm-up time (including "bright-emitter" or "dull-emitter")
•  by characteristic curves design (e.g., sharp- versus remote-cutoff in some pentodes)
•  by application (receiving tubes, transmitting tubes, amplifying or switching, rectification, mixing)
•  specialized parameters (long life, very low micro phonic sensitivity and low-noise audio amplification, rugged or military versions)
•  specialized functions (light or radiation detectors, video imaging tubes)

** tubes used to display information (Nixie tubes, "magic eye" tubes, vacuum fluorescent displays, CRTs)
Tubes have different functions, such as cathode ray tubes which create a beam of electrons for display purposes (such as the television picture tube)

Within the space of a mere fourteen years, television has developed from a scientific toy to a public service which daily provides entertainment and instruction to hundreds of thousands of people on both sides of the Atlantic. The skepticism which originally prevailed concerning the possibility of exploiting the new art has given place to complete confidence in both technical and commercial circles, and television now supports a thriving industry which is assured, by plans already well advanced, of rapid growth and development not only in Great Britain and in the U.S.A. but also in European countries which, s o far, have not instituted a television service.

Many problems had to be solved before television could been brought to its state of perfection at which, from the technical point of view, mass popularity can be assured. But mass popularity depends not only upon technical perfection but also upon the availability of receivers of good performance at low cost. The production of such equipment was, of course, the task of the set maker. In the design of high-quality television receivers, the tubes employed played an important part.

+ Tubes originally produced for normal broadcast reception, however efficient they may be for that purpose, are not necessarily the most suitable for television reception. Indeed, such have been  developments that it is safe to say that unless tubes which have been specially developed for television service are employed, receivers of the highest performance combined with low cost cannot be realized.

HERE below the Datasheets Manuals of the  Thermionic tubes used in the TV SET in the article:REX (ZANUSSI) MOD. RB24  CHASSIS  BS212.4

REX (ZANUSSI) MOD. RB24  CHASSIS  BS212.4  CONTACTLESS TOUCH SENSOR PROGRAM CHANGE KEYBOARD CIRCUIT ARRANGEMENT FOR ESTABLISHING A CONSTANT POTENTIAL OF THE CHASSIS OF AN ELECTRICAL DEVICE WITH RELATION TO GROUND :


Circuit arrangement for establishing a reference potential of a chassis of an electrical device such as a radio and/or TV receiver, such device being provided with at least one contactless touching switch operating under the AC voltage principle. The device is switched by touching a unipole touching field in a contactless manner so as to establish connection to a grounded network pole. The circuit arrangement includes in combination an electronic blocking switch and a unidirectional rectifier which separates such switch from the network during the blocking phase.


1. A circuit arrangement for establishing, at the chassis of an electrical device powered by a grounded AC supply network, a reference potential with relation to ground, said device having at least one contactless touching switch operating on the AC voltage principle, the switch being operated by touching a unipole touching field in a contactless manner, said arrangement comprising an electronic switch for selectively blocking the circuit of the device from the supply network, a half-wave rectifier including a pair of diodes individually connected in series-aiding relation between the terminals of the supply network and the terminals of the device for separating the electronic blocking switch from the supply network during a blocking phase defined by a prescribed half period of the AC cycle, and a pair of condensers individually connected in parallel with the respective diodes. 2. A circuit arrangement according to claim 1, wherein the capacitances of the two condensers are of equal magnitude.

Description:

This invention relates to a circuit arrangement for establishing a constant reference potential on the chassis of an electrical instrument such as a radio and/or a TV receiver. Such instrument includes at least one contactless touching switch operating under the AC voltage principle, whereby by touching a single pole touching field the contactless switch is operated.

In electronic devices, for example TV and radio receivers, there are used in ever increasing numbers electronic touching switches for switching and adjusting the functions of the device. In one known embodiment of this type of touching switch, which operates on a DC voltage principle, the function of the electronic device, is contactlessly switched by touching a unipole touching field, the switching being carried out by means of an alternating current voltage. When using such a unipole touching electrode, one takes advantage of the fact that the AC current circuit is generally unipolarly grounded. In order to close the circuit by touching the touching surface via the body of the operator to ground, it is necessary to provide an AC voltage on the touching field. In one special known embodiment there is employed a known bridge current rectifier for the current supply. This type of arrangement has the drawback that the chassis of the device changes its polarity relative to the grounded network pole with the network frequency. With such construction considerable difficulties appear when connecting measuring instruments to the device, such difficulties possibly eventually leading to the destruction of individual parts of the electronic device.

In order to avoid these drawbacks, the present invention provides a normal combination of a unidirectional rectifier with an electronic blocking switch that separates the chassis of the electronic device from the network during the blocking phase. In accordance with the present invention, the polarity of the chassis of the electronic device does not periodically change, because the electronic device is practically separated from the network during the blocking phase of the unidirectional rectifier by means of the electronic blocking switch.

In a further embodiment of the invention a further rectifier is connected in series with the unidirectional rectifier in the connection between the circuit and the negative pole of the chassis. Such further rectifier is preferably a diode which is switched in the transfer direction of the unidirectional rectifier. According to another feature of the invention there are provided condensers, a respective condenser being connected parallel with each of the rectifiers. Preferably the two condensers have equal capacitances. Because of the use of such condensers, which are required because of high frequency reasons, during the blocking phase there is conducted to the chassis of the electronic device an AC voltage proportional to the order of capacitances of the condensers. Thus there is placed upon the touching field in a desired manner an AC voltage, and there is thereby assured a secure functioning of the adjustment of the device when such touching occurs.

In the embodiment of the invention employing two rectifiers there is the further advantage that over a bridging over of the minus conduit of the rectifier that is connected between the network and the negative pole of the chassis connection, no injuries can be caused by a measuring instrument in the electronic device itself and in the circuit arrangement connected thereto.

In the accompanying drawing:

The sole FIGURE of the drawing is a circuit diagram of a preferred embodiment of the invention.

In the illustrated embodiment the current supply part of the device, shown at the left, is connected via connecting terminals A and B to an AC voltage source, the terminal B being grounded at 8. The current supply part consists of a unidirectional rectifier in the form of a diode 1 with its anode connected to the terminal I, the cathode of diode 1 being connected to one input terminal 9 of an electronic device 2. In the device 2 there is also arranged a sensor circuit 3, shown here mainly as a block, circuit 3 being shown as including a pnp input transistor the emitter of which is connected to an output terminal 11 of the device 2. The collector of such transistor is connected to the other output terminal 12 of the device 2. The base of the transistor is connected by a wire 13 to a unipolar touching field 4 which may be in the form of a simple metal plate instead of the pnp transistor shown, the sensor circuit itself may consist of a standard integrating circuit which controls, among other things, the periodic sequential switching during the touching time of the touching field 4. All of the circuits of the electronic device 2 are isolated in a known manner from the chassis potential. Between the network terminal B and the negative pole 10 of the chassis there is arranged in the direction opposite that of diode 1 a further diode 5, the anode of diode 5 being connected to the terminal 10, and the cathode of diode 5 being connected to the terminal B of the current supply. To provide for HF type bridging of the diodes 1 and 5 there are arranged condensers 6 and 7 respectively, which are connected in parallel with such diodes.

The invention functions by reason of the fact that in an AC network separate devices radiate electromagnetic waves which produce freely traveling fields in the body of the person who is operating and/or adjusting the device, thereby producing an alternating current through his body to ground, as indicated by the - line at the right of the circuit diagram. If now the person operating the device touches the switching field 4, then the pnp type input transistor of the sensor circuit 3, which is placed on a definite reference potential (for example 12 Volts) and is connected with the negative halfwave of the AC voltage potential, is made conductive. There is thereby released a control command in the sequential switching, for example, for switching the electronic device to the next receiving channel. It is understood that the most suitable connection is formed between ground and the touching field 4 by means of a wire. By the use of such wires it would be assured that in all cases the base of the transistor in circuit 3 is connected to ground. This would, however, not permit anyone to operate the switch without the use of an auxiliary means such as a wire. It will be assumed that the touching almost always results directly via the almost isolated human body. For this reason the AC current fields are necessary, because otherwise there cannot always be provided a ground contact. Thus this connection is established via the body resistance of the person carrying out the touching of the switch.

The positive half wave of the alternating current travels to the terminal 9 of the electronic device 2 after such current has been rectified and smoothed by the devices 1, 6. Such positive halfwave is also conducted to the sensor circuit 3. The thus formed current circuit is closed by way of the chassis of the electronic device 3, the diode 5, and the terminal B. When there is a negative halfwave of the alternating current delivered by the current supply, both diodes 1 and 5 remain closed so that the chassis of the device 2 remains separated from the network during the blocking phase. Nevertheless, by means of condensers 6 and 7 the chassis is placed in a definite network potential, which depends on the relationship of the order of magnitude of the two condensers 6 and 7. When the capacitances of such condensers are equal, there is placed upon the chassis of the device 2 the constant reference potential, and simultaneously there is present via the sensor circuit 3 the required AC voltage at the touching field 4 for adjusting the function or functions of the device 2 upon the touching of the touching field 4.

The reference character 15 indicates a terminal or point at which the potential of the chassis of the device 2 may be measured. As above explained, the diode 5 causes the potential of the chassis at 15 to be separated from the network ground when a negative AC halfwave arrives. It will be noted that the return conduit of the circuit is held at a fixed chassis potential. The input transistor of the sensor circuit 3 remains, however, locked because it is subjected to a DC current of about 12 volts. If now, by means of touching the touching field 4, the chassis potential is connected to ground, then the transistor switches through and releases a switching function.

If the connecting terminals AB of the current source are exchanged, as by changing the plug, then there is still secured the condition that the chassis of the device is separated from the network ground via the diode, in this case the diode 1. The reference potential of the chassis consequently remains constant and the changing AC fields which are superimposed on the condensers can produce in the touching human body an AC current voltage due to the fields which are radiated by the device.

A suitable sensor which may be employed for the circuit 3 herein may be a sensor known as the "SAS 560 Tastatur IS," manufactured and sold by Siemens AG.

It is to be understood that the present invention is not limited to the illustrated environment. They can also be used in electronic blocking switch including a Thyristor circuit, which in the same manner separates the electronic device during the blocking phase from the network rectifier. With such Thyristor circuit the drawbacks described in the introductory portion of the specification of known circuit arrangements are also avoided.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

Note the EHT selenium rectifier which is a Specially designed selenium rectifiers were once widely used as EHT rectifiers in television sets and photocopiers. A layer of selenium was applied to a sheet of soft iron foil, and thousands of tiny discs (typically 2mm diameter) were punched out of this and assembled as "stacks" inside ceramic tubes. Rectifiers capable of supplying tens of thousands of volts could be made this way. Their internal resistance was extremely high, but most EHT applications only required a few hundred microamps at most, so this was not normally an issue. With the development of inexpensive high voltage silicon rectifiers, this technology has fallen into disuse.A conventional selenium rectifier consists of a metal plate, which acts as the rectifier base electrode, upon one side of which there are deposited, usually by evaporation techniques, layers of selenium with either a halogen additive, such as chlorine, or doped with a metal such as gallium or indium, or both an additive and a dopant. These layers of selenium may be sandwiched with relatively thin layers of various metals such as nickel between the selenium and the base electrode. The counter electrode is generally an alloy such as a cadmium tin alloy. Rectification takes place in a barrier layer which is adjacent the counter electrode. Such rectifiers are reliable but the evaporation apparatus is costly to install and maintain.

SUMMARY OF THE INVENTION
It is an object of the present invention to provide a selenium rectifier, in which the barrier layer constituted by the amorphous selenium is adjacent the base electrode rather than the counter electrode, by electrophoretically depositing the selenium layers. The electrophoretic deposition of selenium is a relatively rapid process compared with evaporation techniques, and does not require costly apparatus.

According to a broad aspect of the invention, there is provided a selenium rectifier comprising a metal plate base electrode; at least one metal layer deposited on one surface of said metal plate, said metal layer consisting of a metal different than that of said metal plate; a first layer of amorphous selenium on said at least one metal layer; a second layer of selenium containing a first halogen additive, said second layer deposited on said first layer; a third layer of selenium containing a second halogen additive and a metallic dopant, said third layer deposited on said second layer; and a metal counter electrode layer deposited on said third layer.