NUCLEAR RADIO TV (PRANDONI) MOD.250 YEAR 1976.

The NUCLEAR RADIO TV (PRANDONI) MOD.250 Is a portable 12" B/W television with
6 programs VHF /  UHF  and potentiometers keyboard integrated tuning search system.
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.


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.


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.


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.
It was possible to power it with mains or 12 volt source and it has even antennas for VHF and UHF channels.

It has a Transistorized horizontal deflection circuits  made up of a horizontal switching or output transistor, a diode, one or more capacitors and a deflection winding. The output transistor, operating as a switch, is driven by a horizontal rate square wave signal and conducts during a portion of the horizontal trace interval. A diode, connected in parallel with the transistor, conducts during the remainder of the trace interval. A retrace capacitor and the deflection yoke winding are coupled in parallel across the transistor-diode combination. Energy is transferred into and out of the deflection winding via the diode and output transistor during the trace interval and via the retrace capacitor during the retrace interval.
In some television receivers, the collector of the horizontal output transistor is coupled to the B+ power supply through the primary windings of the high voltage transformer.

Unusual it's design but was a must in the 70's.

These sets were cheap but well made and reliable.

This kind of simple and fair isn't today anymore (even in people).




TRANS CONTINENTS / OCEANIC / PRANDONI was an Italian manufacturer of radio and after of televison sets.

It was also the owner of brands like Trans Continents and Nuclear radio TV or simply Nuclear.

"Prandoni S.p.A." was founded by Dario Prandoni. Finally his son Giorgio Prandoni sold the company to the French "Thomson".

In 1998 Francesco Juilland and Giorgio Prandoni co-founded "Mediacube USA, Inc.", a film production company and a visual effects service provider in USA, Europe and in Italy.
a film production company and a visual effects service provider in USA, Europe and in Italy.

Giorgio Prandoni is a leading figure and heir to the most prestigious industrialist dynasty in the design and manufacture of radio equipment and multi standard television sets in Italy. (His father was Dario Prandoni the luminary owner of Prandoni S.p.A. one of Europe's most highly regarded electronic companies;


Dario Prandoni formed the basis of the Prandoni Empire and Giorgio Prandoni sells the company in France to Thomson with a big one deal). During his tenure from 1998 to February 2002 as Mediacube's CEO Francesco Juilland has created important joint venture between Mediacube USA, Inc. and important European, American and Canadian companies. He also brokered the acquisition of a share of Minerva Pictures (Italy) they own a library of more than 1,500 titles of which 850 are for worldwide rights in perpetuity. The titles include classics works by Pasolini, Germi, Bellocchio, Godard, Fellini, Antonioni and others. Most recently in 2000, Francesco Juilland was elected in the Board of Directors of Ionic WW Studios, a fully digital Hollywood studio organized and financed by Mediacube as Major Investor together with Giorgio Prandoni and Javier Rodriguez, Spanish businessman and scion of an important and conservative Family of Spain full of history and tradition and thank to the greenlight of a guardian angel like the economist Mr. Diego Colombo, chairman of the Colombo Group with offices in Switzerland and around the world and longtime serious advisor of the Juilland family office. Francesco Juilland is in the Board of Directors with the man that he considers his American mentor Mike Medavoy (producer, former chairman of Tristar Pictures and a legendary "Hollywood industry hero" as Fox News channel calls him, many times Oscars winner, his movies including the masterpieces Apocalypse Now, Philadelphia, Dance with wolves, Who flew over the Cuckoo's nest, Annie Hall, Platoon, Rocky, the Sting, Silence of the lambs, Amadeus, The Terminator, Sleepless in Seattle) and Norman Pattiz (called from "USA Today" and "LA Times" The Ted Turner of the radio) and Arnold Messer (president of Phoenix Pictures, company producer of Larry Flint, The thin red line, U-Turn, The 6th Day, Basic, Holes, Stealth, All the King's men), together with David Hayden and Gigi Pritzker (film producer with Deborah del Prete of "the Wedding Planner" with Jennifer Lopez)