Awesome chassis this.
A portable 12 inches B/W type with fully modular chassis with interchangeable mini cards units on 2 levels montage layout.
On top are fitted all power circuits and on the down side all signal cards units.
Italians sometimes are awesome.
Power
supply is realized with mains transformer and Linear transistorized
power supply stabilizer, A DC power supply apparatus includes a
rectifier circuit which rectifies an input commercial AC voltage. The
rectifier output voltage is smoothed in a smoothing capacitor. Voltage
stabilization is provided in the stabilizing circuits by the use of
Zener diode circuits to provide biasing to control the
collector-emitter paths of respective transistors.A linear regulator
circuit according to an embodiment of the present invention has an
input node receiving an unregulated voltage and an output node
providing a regulated voltage. The linear regulator circuit includes a
voltage regulator, a bias circuit, and a current control device.

In
one embodiment, the current control device is implemented as an NPN
bipolar junction transistor (BJT) having a collector electrode forming
the input node of the linear regulator circuit, an emitter electrode
coupled to the input of the voltage regulator, and a base electrode
coupled to the second terminal of the bias circuit. A first capacitor
may be coupled between the input and reference terminals of the voltage
regulator and a second capacitor may be coupled between the output and
reference terminals of the voltage regulator. The voltage regulator
may be implemented as known to those skilled in the art, such as an LDO
or non-LDO 3-terminal regulator or the like.
The bias circuit
may include a bias device and a current source. The bias device has a
first terminal coupled to the output terminal of the voltage regulator
and a second terminal coupled to the control electrode of the current
control device. The current source has an input coupled to the first
current electrode of the current control device and an output coupled
to the second terminal of the bias device. A capacitor may be coupled
between the first and second terminals of the bias device.
In the
bias device and current source embodiment, the bias device may be
implemented as a Zener diode, one or more diodes coupled in series, at
least one light emitting diode, or any other bias device which develops
sufficient voltage while receiving current from the current source. The
current source may be implemented with a PNP BJT having its collector
electrode coupled to the second terminal of the bias device, at least
one first resistor having a first end coupled to the emitter electrode
of the PNP BJT and a second end, a Zener diode and a second resistor.
The Zener diode has an anode coupled to the base electrode of the PNP
BJT and a cathode coupled to the second end of the first resistor. The
second resistor has a first end coupled to the anode of the Zener diode
and a second end coupled to the reference terminal of the voltage
regulator. A second Zener diode may be included having an anode coupled
to the cathode of the first Zener diode and a cathode coupled to the
first current electrode of the current control device.

A circuit
is discl
osed for improving operation of a linear regulator, having an
input terminal, an output terminal, and a reference terminal. The
circuit includes an input node, a transistor, a bias circuit, and first
and second capacitors. The transistor has a first current electrode
coupled to the input node, a second current electrode for coupling to
the input terminal of the linear regulator, and a control electrode. The
bias circuit has a first terminal for coupling to the output terminal
of the linear regulator and a second terminal coupled to the control
electrode of the transistor. The first capacitor is for coupling between
the input and reference terminals of the linear regulator, and the
second capacitor is for coupling between the output and reference
terminals of the linear regulator. The bias circuit develops a voltage
sufficient to drive the control terminal of the transistor and to
operate the linear regulator. The bias circuit may be a battery, a bias
device and a current source, a floating power supply, a charge pump, or
any combination thereof. The transistor may be implemented as a BJT or
FET or any other suitable current controlled device.

Power
Supply: The examples chosen are taken from manufacturers' circuit
diagrams and are usually simplified to emphasise the fundamental nature
of the circuit. For each example the particular transistor properties
that are exploited to achieve the desired performance are made clear. As
a rough and ready classification the circuits are arranged in order of
frequency: this part is devoted to circuits used at zero frequency,
field frequency and audio frequencies. Series Regulator Circuit Portable
television receivers are designed to operate from batteries (usually
12V car batteries) and from the a.c. mains. The receiver usually has an
11V supply line, and circuitry is required to ensure that the supply
line is at this voltage whether the power source is a battery or the
mains. The supply line also needs to have good regulation, i.e. a low
output resistance, to ensure that the voltage remains constant in spite
of variations in the mean current taken by some of the stages in the
receiver. Fig. 1 shows a typical circuit of the power -supply
arrangements. The mains transformer and bridge rectifier are designed to
deliver about 16V. The battery can be assumed to give just over 12V.
Both feed the regulator circuit Trl, Tr2, Tr3, which gives an 11V output
and can be regarded as a three -stage direct -coupled amplifier. The
first stage Tr 1 is required to give an output current proportional to
the difference between two voltages, one being a constant voltage
derived from the voltage reference diode D I (which is biased via R3
from the stabilised supply). The second voltage is obtained from a
preset potential divider connected across the output of the unit, and is
therefore a sample of the output voltage. In effect therefore Tr 1
compares the output voltage of the unit with a fixed voltage and gives
an output current proportional to the difference between them. Clearly a
field-effect transistor could do this, but the low input resistance of a
bipolar transistor is no disadvantage and it can give a current output
many times that of a field-effect transistor and is generally preferred
therefore. The output current of the first stage is amplified by the two
subsequent stages and then becomes the output current of the unit.
Clearly therefore Tr2 and Tr3 should be current amplifiers and they
normally take the form of emitter followers or common emitter stages
(which have the same current gain). By adjusting the preset control we
can alter the fraction of the output voltage' applied to the first stage
and can thus set the output voltage of the unit at any desired value
within a certain range. By making assumptions about the current gain of
the transistors we can calculate the degree of regulation obtainable.
For example, suppose the gain of Tr2 and Tr3 in cascade is 1,000, and
that the current output demanded from the unit changes by 0.1A (for
example due to the disconnection of part of the load). The corresponding
change in Tr l's collector current is 0.1mA and, if the standing
collector current of Tr 1 is 1mA, then its mutual conductance is
approximately 4OmA/V and the base voltage must change by 2.5mV to bring
about the required change in collector current. If the preset potential
divider feeds one half of the output voltage to Tr l's base, then the
change in output voltage must be 5mV. Thus an 0.1A change in output
current brings about only 5mV change in output voltage: this represents
an output resistance of only 0.0552.
How AFC Circuit Works in B/W Analog Television Receiver:

Push-Button
tuning on u.h.f. while being very convenient often leaves a margin of
mistuning, especially after some wear and tear has occurred on the
mechanism. Even dial tuning can lead to errors due to the difficulty
many people experience in judging the correct point. Oscillator drift
due to temperature changes can also cause mistuning. Automatic frequency
control (a.f.c.) will correct all these faults. The vision carrier when
the set is correctly tuned on u.h.f. is at 39.5MHz as it passes down
the i.f. strip. Thus if at the end of the i.f. strip a discriminator
tuned circuit is incorporated centred on 39.5MHz the discriminator
output will be zero at 39.5MHz and will move positively' one side of
39.5MHz and negatively the other as the tuning drifts. This response is
shown in Fig. 1.
If the tuning is not correct then the
discriminator output is not zero and if this output is applied to change
the reverse bias on a tuning diode mounted in the oscillator section of
the u.h.f. tuner it will correct most of the error. Tuning, varicap or
varactor diodes-to give them a few of their names-are junction diodes
normally operated with reverse bias but not sufficient to bias them into
the breakdown region in which zener diodes operate. The greater the
reverse bias the lower their capacitance: a typical curve, for the
PHILIPS BB105 or STC BA141 tuning diode, is shown in Fig. 2. All diodes e

xhibit
this basic type of characteristic but special diodes have to be used
for u.h.f. because they must not introduce any excessive loss into the
tuned circuits they control. In other words, just as a coil has to have a
good Q so does a varicap diode. Normally, we don't worry about the Q of
a capacitor as it is usually very good. However, a tuning diode is not a
true capacitor. It has, for example, leakage current so the Q of the
diode is a factor which has to be considered. The diode manufacturer
however will have considered these points and if you buy a diode
specified for u.h.f. use you will have no trouble. These points have
been mentioned to clear up any misunderstandings and to show why any old
diode won't do.
Basic AFC SystemTo return to our TV
set, if the oscillator frequency is too high then the vision carrier
frequency will also be too high and in the simple arrangement shown in
Fig. 3 the discriminator will give a negative signal to decrease the
bias on the tuning diode thus increasing its

capacitance
and in turn reducing the oscillator frequency and correcting the error.
Note that in this diagram the reverse bias on the diode is applied to
its cathode. It is therefore positive with respect to ground so that a
negative signal from the discriminator will reduce the positive voltage
on the diode thus reducing its bias and increasing its capacitance. In
this arrangement the diode is biased somewhere near the mid point of its
characteristic by the positive d.c. bias fed into one side of the
discriminator. The discriminator thus adds to or subtracts from this
d.c. bias.
AFC Loop Gain:The amount by which the error
is reduced depends on the gain of the circuit. An estimate of the gain
required must first be made by guessing how much error is likely to be
given by your push -buttons or hand tuning: 1MHz would be an outside
figure as a tuning error of that magnitude would produce a very bad
picture of low definition in one direction and badly broken up in the
other. This error should be reduced to

about
100kHz to be really unnoticeable, indicating a required gain of ten. In
fitting a.f.c. to an existing set some measure- ments should be done as
an experiment before finally deciding on the circuit gain. The first
thing to do is to add the suggested discriminator to the i.f. strip. As
the circuit (Fig. 4) shows a Foster -Seeley type discriminator is used
and with the coils specified and the driver circuit shown it should give
±4V for 0.5MHz input variation.
EXAMPLE of Circuit Description:The
driver stage Tr1 takes a small sample signal from the i.f. strip but
this should be large enough to drive Tr1 into saturation. That is to say
Tr1 is a limiter stage so that the signal amplitude applied to the
discriminator coil L2 stays constant over the normal range of signal
levels. Trl is biased at approximately 7mA which, according to the
original report ("Simple a.f.c. system for 625 -line TV receivers" by P.
Bissmire, PHILIPS Technical Communications, March, 1970), gives the
best limiting performance. C1, R

14
and R3 damp the stage to prevent oscillation. C2 decouples the power
feed and should be close to the circuit. The coil former and can are the
normal ones used for TV sets and so should be easily obtainable: the
former diameter is 5mm. and length 40mm. and winding details are given
in Fig. 5.
The invention being
thus described, it will be obvious that the same may be varied in many
ways. Such variations are not to be regarded as a departure from the
spirit and scope of the invention, and all such modifications as would
be obvious to one skilled in the art are intended to be included within
the scope of the developed apparates both tubes or transistors.
The CRT Tube is a FIVRE 12 B 121 type.
The TUBE CRT TUBE FIVRE 12B 121
is fabricated by an extint Italian manufacturer.
It's a 120° degree type so it's very compact.
FIVRE WAS Fabbrica Italiana Valvole Radio Elettriche which was fabricating Picture tubes and Radio Tubes.
FIVRE were established in 1932 as a manufacturer of thermoinic valves.
Cathode ray tubes for monochrome television sets were introduced in 1952.Since then, many millions of FIVRE CRTs have been incorporated in TV sets by most European brand leaders.
In 1976 FIVRE extendet the product rance to include monochrome data display tubes, gaining in a short time a large share of the European market.
The FIVRE range of CRT are used in applications demanding a quality product, in both the civil and military areas, including: high-resolution graphics and desk-top-publishing, radar, large screen dispays and medical equipment; to name but a few.
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