MIVAR TELEVISORE 24" T45 CHASSIS TV705 / TV708 INTERNAL VIEW

The MIVAR chassis series TV705 / TV708 is the last MIVAR tv chassis with tubes, and last model with hand wired chassis parts and last model series of MIVAR tv with wooden cabinet for B/W screen series.


It's divided in sections providing Signal processing with full discretes components, synch separation even with discrete components and FRAME deflection with output transformer and a completely hand wired Line deflection + EHT stages on the right side.

Power supply is located on the left side of the chassis which is a heavy steel basis.

The chassis is entirely developed by MIVAR and around PHILIPS semiconductors and it's not a crappy copy from another cheap crap around recognizeable even in that era.


Tubes used:

- PY88
- PL504
- PCL805

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:MIVAR  TELEVISORE  24" T45  

 

 
- The EHT Output is realized with a selenium rectifier.

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 selenium rectifier is a type of metal rectifier, invented in 1933. They were used to replace vacuum tube rectifiers in power supplies for electronic equipment, and in high current battery charger applications.

The photoelectric and rectifying properties of selenium were observed by C. E. Fitts around 1886 but practical rectifier devices were not manufactured routinely until the 1930s. Compared with the earlier copper oxide rectifier, the selenium cell could withstand higher voltage but at a lower current capacity per unit area.