MIVAR TELEVISORE 24" T45 YEAR 1972.

The MIVAR  TELEVISORE  24" T45 is A model of 24 inches B/W screen with 7 programs preselection with a very big push buttons mechanic keyboard which incorporates big potentiometers for tuning search.


The invention relates to a tuning unit with bandswitch for high frequency receivers, especially radio and television receivers, having a potentiometer system for the control of capacity diodes, the said potentiometer system consisting of a plurality of parallel resistance paths along which wiper contacts can be driven by means of screw spindles disposed adjacent one another in a common insulating material housing in which a bandswitch formed of metal rods is associated with each tuning spindle.
In these tuning units, the working voltages of the capacity diodes in the tuning circuits are recorded once a precise tuning to the desired frequency has been performed. A potentiometer tuning system has great advantages over the formerly used channel selectors operating with mechanically adjustable capacitors (tuning condensers) or mechanically adjustable inductances (variometers), mainly because it is not required to have such great precision in its tuning mechanism.
Tuning units with bandswitches formed of variable resistances and combined with interlocking pushbuttons controlling the supply of recorded working voltages to capacity diodes are known. Channel selection is accomplished by depressing the knobs, and the tuning or fine tuning are performed by turning the knobs. The resistances serving as voltage dividers in these tuning units are combined into a component unit such that they are in the form of a ladderlike pattern on a common insulating plate forming the cover of the housing in which the tuning spindles and wiper contacts corresponding to the variable resistances are housed. The number of resistances corresponds to the number of channels or frequencies which are to be recorded. The wiper contact picks up a voltage which, when applied to the capacity diodes determines their capacitance and hence the frequency of the corresponding oscillating circuit. The adjustment of the wipers is performed by turning the tuning spindle coupled to the tuning knob. By the depression of a button the electrical connection between a contact rod and a tuning spindle is brought about and thus the selected voltage is applied to the capacity diodes. Since the push buttons release one another, it is possible simply by depressing another button to tune to a different receiving frequency or a different channel, as the case may be.
 Moreover, using this arrangement, the only indication--during adjustment--of which channel is selected is by station identification.

 The mechanical turret approach to television tuning has been used almost exclusively for the past 60 years. Even though replete with the inherent disadvantages of mechanical complexity, unreliability and cost, such apparatus has been technically capable of performing its intended function and as a result the consumer has had to bear the burdens associated with the device. However, with the " recent "  Broadcast demands for parity of tuning for UHF and VHF channels, the increasing number of UHF and cable TV stations have imposed new tuning performance requirements which severely tax the capability of the mechanical turret tuner. Consequently, attempts are now being made to provide all electronic tuning to meet the new requirements.

In the end of the 60's increasingly attention was focused on the varicap diode tuner as the latest, sophisticated means of television receiver frontend tuning in both colour and black and white sets.
The main purpose of this article is to investigate the servicing problems associated with this comparatively new method of tuning.
First however let's briefly recap on the principles involved in this tuning system:
The tuners use variable capacitance (or "varicap") diodes as the variable tuning elements: the effective capacitance of the diodes is controlled by the reverse bias applied across them, tuning being achieved by varying this voltage. As the reverse bias across a varicap diode is increased so its junction depletion region widens thus reducing its capacitance.

A VHF/ UHF television tuner is constructed in accordance with the present invention includes a preselector tuned circuit having a solid state voltage controlled capacitor as its tunable element, a radio frequency amplifier coupled to the preselector circuit and alsoother circuit to perfect the signal receiving capability and the application the like.


Considering the Mechanical Tuner Problems:

To get the servicing problems in perspective let us next consider the tuning arrangements previously used.
The earliest of these, employed on v.h.f., was the switched tuner which was either of the turret or incremental type.
 The turret tuner substituted a coil bearing "biscuit" mounted on the rotating drum or turret when channels were changed. Twelve positions were normally provided, with a fine tuning knob to adjust the local oscillator frequency. As its name suggests the incremental tuner simply added more inductance to the tuned circuits at every downward channel movement: thus the highest inductance was present on channel one and the least on channel 12 (which normally covered 13 as well with manipulation of the fine tuner).

The movement towards u.h.f. TV working, initially with dual standard sets and later with single standard ones, brought about the need for u.h.f. tuners. In the earliest u.h.f. receivers valve tuners which were not particularly efficient were used.

The drive mechanism was usually a dual speed rotary system calibrated from channels 21 to 68. Experience in the field indicated that 625 line television was in many cases considered by the viewer to be inferior to 405 -line reception, on account of the poor signal to noise ratio achieved by the valve tuners. Many viewers were not prepared to use external u.h.f. aerials of course, having achieved satisfactory reception on v.h.f. with an indoor aerial: this aggravated the situation even more.
Another aspect which caused difficulty was the care needed to tune in a u.h.f. channel using a rotary tuner covering the whole of Bands IV and V. Many viewers simply could not tune in BBC 2 or ZDF or ORF or any channel correctly with such a tuning mechanism, finding that they had passed right over the channel they wanted before realising what they had done.
The advent of transistor tuners rapidly improved the quality of u.h.f. reception but use of a rotary mechanism was continued by many manufacturers. Thus while potential reception was improved the same tuning difficulties remained and viewers continued to gravitate towards 405 line viewing using the "old faithful" switched tuner. The operational breakthrough came with the introduction of the push-button u.h.f. channel change.
The mechanism is basically simple. Adjustable push buttons press down on a lever bar which in turn rotates the tuner's variable capacitors to the appropriate position. Each button is capable of tuning over the entire u.h.f. bands and this leads to customer confusion at times when after some adjustments which were too heavy handed they find themselves receiving ITV on a BBC button or a ORF and ZDF broadcasting or any channel possible !


Mechanical Faults:
Mechanical tuning obviously has its snags. There are for example contact springs which earth the tuning capacitor and go intermittent. This gives rise to the most random tuning defects, capable of driving the. most patient viewer to a state of total exasperation. It is also possible for the rotation mechanism to hang up and jam intermittently, or just become sticky, so that the reset accuracy of the mechanism is impaired and the receiver has to be retuned every time the channel is changed.
The vanes in the tuning capacitor can also short out at different settings, thereby eliminating some channels. The Varicap Tuner It will be seen then that mechanical defects can cause very irritating fault symptoms. If one thinks along the lines that anything mechanical is nasty, then the elimination of mechanical parts can only be to the good.
The logic of this is splendid provided the electronic replacement for the mechanical system is more reliable! Otherwise we are leaping out of the frying pan into the fire! In the light of experience gained with mechanical tuning devices it seems great that with the varicap tuner we have at last dispensed with the dreaded rotary tuning capacitor, replacing it instead with a variable voltage to the tuner.

Let us think about this however since things are never quite as simple as they first appear. The tuning voltage has to be variable in order to tune the receiver. Obviously then a means of varying the voltage has to be provided to act as the tuning control.

As it is a voltage that has to be varied the tuning control takes the form of a potentiometer., Now we have returned to a mechanical system again, though in a less complex form.

A potentiometer is required for each channel, selected by pressing the appropriate channel button. We have lost a tuning capacitor and its rotating mechanism and gained a set of pots and selector switches therefore. Provided the pots and switches are mechanically more reliable than the tuning capacitor we should be better off-or should we?


Need for Voltage Stabilisation.

The voltage selected by the pots cannot be allowed to drift otherwise the receiver will go off -tune. The voltage supply to the potentiometers has to be stabilised therefore and a stabilising zener diode or integrated circuit (TAA550) .is needed for this purpose.
Any failure in this part of the circuit will give rise to tuning drift or worse, a total loss of reception. A short-circuit TAA550 for example will completely remove the tuning voltage while if it is open circuit the tuning can vary with picture brightness. Likewise any intermittency in the potentiometers or associated switching and/or resistors can also cause problems.


Relative Reliability of Tuners:
It will be seen then that in order to lose our troublesome mechanical arrangement we have had to introduce considerably more electronics which we trust are going to be more reliable. In addition we have not so far considered the relative reliability of the varicap tuner itself compared with the mechanical type. Since two r.f. transistors are generally used to compensate for the reduced Q of the varicap tuned circuits we immediately have twice the likelihood of an r.f. stage breaking down!
And being semiconductors the varicap diodes themselves are more likely to fail than the sections of a ganged tuning capacitor. It is reasonable then to conclude that if mechanical faults are the most prevalent the use of varicap tuners will make life easier. Mechanical faults are generally not too difficult to sort out however and the field engineer can often cope with them in the home.
Can the same be said of the varicap tuner? It seems that this type of tuner does not need so much attention as its mechanical counterpart but is likely to throw up some much more difficult faults when it does, resulting in bench repairs being needed. So far my own experience has indicated that varicap tuning faults nearly always need servicing on the bench.
Generally speaking it seems true to say that varicap tuners themselves are adequately reliable: the snags result from the tuning system and stabilised power supply.


Tuning Drift with Varicap Tuners:
If a varicap tuned receiver is constantly drifting off tune the +30V supply should be the number one suspect. It is best to connect an Avometer permanently to the supply so that it can be precisely monitored-if necessary write down the exact voltage measured.
If the receiver drifts, check the voltage. If it has changed, even slightly, this may well be enough to be the cause of the fault. To pinpoint and confirm the diagnosis aerosol freezer should be applied to the stabiliser i.c. or zener. If the voltage returns to normal or changes wildly for the worse the stabiliser is almost certainly the cause of the trouble and should be replaced.
A prolonged soak test should then be carried out. Another point concerning varicap tuners arises with their use in colour receivers.

 There were  makers of the most expensive colour receiver on the market still didn't use a varicap tuner but instead use a mechanical one. The makers' claim is that the signal to-noise ratio of the varicap tuner is inadequate for their colour standards. Undoubtedly the results obtained on the receiver seem to confirm this. Interestingly, the same manufacturers use varicap tuners in their black -and -white receivers, and the tuning button system is often full of troublesome intermittent contacts. The varicap tuner has its advantages and disadvantages then. Probably the simplest comment would be to say that when it is good it is very very good but when it is bad it is horrid!

The tellye is here shown is the last model with Tubes technology and last model with hand wired chassis parts and last model series of MIVAR with wooden cabinet for B/W screen series.

Even after almost 40 Years it runs fine.

This model was marketed toghether with first MIVAR models with color screen and Delta CRT Tube with same keyboard !!!!

The model is called TELEVISORE 24" T45 which means TELEVISION of 24 Inches T45 and it's fabricated by MIVAR an Italian factory still present toghether with his founder Carlo Vichi a very young man of 88 Years old still working in business.

It's made by MIVAR an Italian Brand no more active since 20/12/2013.


MIVAR is a Factory site in the near of Milan (italy) in a Industrial city conglomerate called Abbiate Grasso.

Founded in 1945 by Mr. Carlo Vichi class of 1923, The activity started in 1945 - in Milano, Via Ugo Tommei 5 street with fabrication of little radio apparates.

HISTORY OF MIVAR.

1945 - Milan, Via Ugo Tommei 5: Begin the activity assembling small radios.

1950 - Via Curtatone 12: developed with the construction of more direct major radio components fabricants.

1956 - 13 Street Strigelli: industrial production is manily targeted to first radio devices with frequency modulation (FM).

1958 - Via P. 30 Jordanians: TV become a reality, the industries is doubling his ACTIVITY, always in Milan, we build the first "real" plant with 400 employees.

1963 - Abbiategrasso, Via Dante 45: in the wake of decentralization and the rampant success of the television, building a facility that will become important in place 800 employees occupying between 1968-70.

1990 - Abbiategrasso Canal towpath: aware of the physiological importance that television plays in society? Modern, rich expertise and resources, we began construction of a factory area of ​​120,000 m? which covered 30.00o , for the viabilit with parking spaces and 60,000 park trees.

In origin the factory was brand named as Radio Var and indeed the tellye here in collection is internally marked as Radio VAR. After 1985 they were marked rightly MIVAR.
Today's activity is oriented in virtual production of LCD crap but with very low market penetration due to "unfair" asian competitors presence and a local governement which don't care about.

(You call it global market, I call it WORLD DESTRUCTION combined toghether with mass Afro scum crap Immigration (EUROPEAN INVASION) to obtain destruction on a large scale in all places and to help more and better the loose of all OUR workplaces and firms , lives, people).

 “If our buildings, our highways, and our railroads should be wrecked, we could rebuild them.

If our cities should be destroyed, out of the very ruins we could erect newer and greater ones.

Even if our armed might should be crushed, we could rear sons who would redeem our power.

Anyway Obsolete Technology Tellye will show even this model as a Time machine which looses nothing of the good tellyes ! ! !

Further Notes:

^ "MIVAR: tutto iniziò in via Tommei", articolo tratto dal sito quattronet.it Archiviato il 14 novembre 2011 in Internet Archive.^ [Maker], Mivar ; Milano from Audiphon to Trader, 703 pictures, 124 sc, su www.radiomuseum.org. URL consultato il 13 giugno 2018.^ NUOVO ASSALTO AL CARROZZONE REL - la Repubblica.it, in Archivio - la Repubblica.it. URL consultato l'11 gennaio 2018.^ LA MIVAR FA UTILI SENZA SPENDERE PER LA PUBBLICITA' - la Repubblica.it, in Archivio - la Repubblica.it. URL consultato l'11 gennaio 2018.^ MIVAR, MIRACOLO AD ABBIATEGRASSO - la Repubblica.it, in Archivio - la Repubblica.it. URL consultato l'11 gennaio 2018.^ Archivio Corriere della Sera, su archiviostorico.corriere.it. URL consultato l'11 gennaio 2018.^ Archivio Corriere della Sera, su archiviostorico.corriere.it. URL consultato l'11 gennaio 2018.^ notizia del sito Adnkronos del 4 maggio 2005 Archiviato il 19 ottobre 2006 in Internet Archive.^ JOB MILANO, in archive.is, 10 dicembre 2012. URL consultato l'11 gennaio 2018 (archiviato dall'url originale il 10 dicembre 2012).^ Mivar rilancia in Full Hd - Il Sole 24 ORE, su www.ilsole24ore.com. URL consultato l'11 gennaio 2018.^ (IT) Mivar In Crisi Ma Il Riscatto Avverrà Con I Led, su www.paid2write.org. URL consultato l'11 gennaio 2018.
MonrifNet, Televisori Mivar: fine dei programmi il 30 novembre - Il Giorno - Legnano, su www.ilgiorno.it. URL consultato l'11 gennaio 2018.
^ “La mia Mivar chiude, l’affitto gratis a chi assume 1200 italiani”, in Fanpage. URL consultato l'11 gennaio 2018.