The TELEFOX MOD. 564/23 MISURINA is a 23 inches B/W Heavy glass television with VHF and UHF channel selectors on rear side and .
Tuning is obtained with rotatable drum selectors for VHF and variable rotatable capacitor for UHF.
A
rotatable drum containing twelve pre-defined channel-specific filters
determines the received channel, where the inductors of the input
matching, the channel filter and the LO tank circuit are changed. The
tuner is divided into two chambers for maximum isolation between the
sensitive RF input and the mixer-oscillator-IF section with its much
larger signals. Also on the drum there are eventually two separate
sub-modules.
It's completely based on tubes technology.
With
this concept, which essentially turned the tuner module into a kind of
Lego building block construction, many different tuners became possible.
Depending upon the country of destination and its associated standard
and IF settings, the required filter modules would be selected. Service
workshops and tv fabricants could later even add or exchange modules
when new channels were introduced, since every inductor module had its
individual factory code and could be ordered separately. As a
consequence more versions of the tuner were produced, covering at least
standards B, B-for-Italy, C. E, F and M.
The
principle of the drum tuner. On an axis two times 12 regularly spaced
channel-specific filter modules are mounted. In front are twelve channel
filter modules for both the channel filter and LO tank circuit tuning.
Seven contacts are available, and one module is shown removed. The
second row contains 12 modules with five contacts for the input filter
circuit. In the tuner module the front section (for mixer-ocillator and
channel filter) is separated by a metal shield from the rear RF input
and pre-amp section. [Philips Service "Documentatie voor de
kanalenkiezers met spoelenwals", 1954]
Examples
of the filter modules as used in the drum tuner. Left the 5-contact
input filter, right the 7-contact BPF and LO tank filters. In both
modules the coils are co-axial for (maximum) mutual coupling.
The
second new valve introduced in the tuners family was the PCF80, a
triode-pentode combo valve specifically designed for the VHF
mixer-oscillator role. First order the circuit principles didn't change
too much from the previous ECC81 based generation, with the triode
acting as a Colpitts oscillator with a tuned feedback from anode to
grid. The oscillator voltage was minimally 5V at the grid, and would be
inductively coupled to the input of the mixer pentode. This inductive
coupling was achieved by putting the oscillator coil S7 and the BPF
coils S5 and S6 on the same rod inside the drum tuner filter modules,
see Fig.5 above. By adjusting the distance between these coils for each
channel filter module, the coupling constant could be kept more or less
constant across all channels, providing as much as possible a
frequency-independent mixer performance. For the mixer the pentode
replaced the previous triode, providing more feedback isolation between
anode and grid. All in all the new tuner must have given a considerable
performance improvement compared to the previous generation.
This brand name "TeleFox" was a semi known to
unknown Italian factory in the 1960's.
They were fabricating cheap tellyes in various models and types with almost one model of chassis circuit for all types.
(TV Set kindly donated to me by Marshal Elia Z.)
The B/W Tubes Television set was powered with a
External Voltage stabiliser unit for Television (portable
metal box) which relates to voltage regulators of the type employed to
supply alternating
current and a constant voltage to a load circuit from a source in which
the line voltage varies. Conventional AC-operated television receivers exhibit several
undesirable performance attributes. For example, under low-line voltage
conditions such as those encountered during peak load periods or
temporary power brown-outs imposed during times of power shortage,
picture shrinkage and defocusing are encountered and under extreme
brown-out conditions the receiver loses synchronization with a resultant
total loss of picture intelligibility.
On the other hand,
abnormally high-line voltage conditions are sometimes encountered, and
this can lead to excessive high voltage and X-ray generation. In
addition, either abnormally high steady state line voltage conditions or
high voltage transients such as those encountered during electrical
storms or during power line switching operations may subject the active
devices and other components of the receiver to over-voltage stresses
which can lead to excessive component failure.
It is a principal
object of the present invention to provide a new and improved
AC-operated television receiver having greatly improved performance
characteristics in the presence of fluctuating power supply voltages.
A
more specific object of the invention is to provide an AC-operated
television receiver affording substantially undegraded performance under
even extremely low-line voltage conditions without excessive high
voltage and X-ray generation under even extremely high-line voltage
conditions.
Still another and extremely important object of the
invention is to provide a new and improved AC-operated television
receiver having greatly improved reliability against component failure. Such regulators are frequently provided
employing saturable core reactors and condensers connected in
circuit... in such manner as to
provide a plurality of variable voltage vectors which vary in different
senses, as the line voltage varies, but which add vectorially in such
manner that t
voltage stabilization
is automatically effected by the provision of an inductive pilot control
device which is adapted to provide two excitation supply voltages for
producing excitation or satuation of two magnetic circuits of a
reversible booster transformer unit or units and diversion of flux from
one magnetic circuit to the other, the booster unit being energized by
primary windings from the A. C. supplysystem and being provided with a
secondary winding or windings connected between the supply system and
the corresponding inain or distribution circuit and in series therewith,
through which a corrective boost voltage is
introduced into the circuit under the influence of the pilot control
device, of an amount equal to that of the supply voltage fluctuation
which initiated it and appropriate in polarity and direction for
restoring the voltage to normal value and providing automatic
stabilization of the circuit voltage against supply voltages which
fluctuate above and below normal value.
Their vector sum remains substantially constant upon
variations in line voltage, for providing automatic voltage
stabilization of single or multiphase A. C. circuits where the supply
voltage and frequency are subject to variation above and below normal
value and where the load is subject to variation between normal limits.
The pilot control device which may be employed singly or may
comprise three units or their equivalent when applied to multiphase
supply systems comprises a pair of closed magnetic circuits or cores
constructed of strip wound magnetic material or stacked laminations, the
two
circuits forming a pair being constructed of materials possessing
dis~similar magnetic characteristics when jointly energized by identical
windings in series or by a collective primary winding, the said
magnetic circuits being suitably proportioned to provide equal fluxes
when energized at normal voltage.
The pilot control device is provided with a main and an auxiliary
secondary winding or group of windings, the main secondary winding or
windings being adapted to provide a voltage representing the difference
in the fluxes of the two circuits to which it is jointly associated,
while
the auxiliary secondary winding embraces only one circuit, preferably
that subject to the least amount of flux variation. Either of the
windings consists of two equal sections or in effect a double winding
with a center tapping to which one end of the single winding is
connected.
The voltage in the single secondary winding of the pilot device becomes
directionally additive to that in one half of the tapped secondary
winding a
nd substractive in respect to that in the other half. When the
supply voltage is normal the voltage provided by the single secondary
winding is zero, since there is no difference of flux in the two magnetic
circuits, and the two excitation voltages
produced in the halves of the other secondary winding are equal and when
connected to the two excitation windings of the booster units, do not
produce any diversion of flux between the two circuits or sets of
circuits in the magnetic system of the booster transformer unit become
equal, and since the series winding on the booster unit is arranged to provide a voltage due to the difference of
the fluxes in its two magnetic circuits or sets of magnetic circuits, no
corrective voltage is introduced into the main circuit by the booster.
If, however, the supply voltage varies from normal the pilot control
device provides a voltage across the one secondary winding due to the
difference in the fluxes of the two dis-similar magnetic circuits of
which it is comprised, which voltage is combined with thosc in the
halves of the other secondary winding to provide two excitation voltages
which vary complementarily to each other as the supply voltage
fluotuates, and cause a transference of flux between the two
circuits or groups of circuits in the booster unit and automatically
provide a corrective boost voltage in the main circuit in which the
series winding of the booster transformer is included of a value equal
to that of the variation in supply voltage which initiated it.
The pilot device may be arranged in various ways, forboth single phase
and multiphase operation, as exemplified by the constructions
hereinafter more fully described.Similarly, numerous arrangements of the
booster transformer unit are possible, some of which are hereinafter
described in detail. The booster transformer unit embodies thc
principles of the inductive devices described in my co-pending
Application No. 411,189, filed February 18, 1954.
As an alternative to the provision of an auxiliary secondary winding on the pilot control device this may be
replaced by an independent or external source of supply,which may be
either subject to or independent of supply voltage variation, provided
such supply may be arranged with a center tapping if required.
Feed-back arrangements may be employed for providing compensation
against voltage drop due to the effects of load in various ways. These
are preferably providedon the booster transformer unit and may comprise a
current transformer in one or more lines of the main circuit,
the secondary output of the transformer being rectified and arranged to
energize an additional excitation winding on the booster transformer
unit which in clfect increases the amount of the corrective boost voltage as the load increases.
A good point on good old B/W Televisions.....................
The Sixties was a time of great change for TV. At
the start of the decade there were just monochrome sets with valves,
designed for 405 -line transmissions at VHF. By the end there was 625
-line colour at UHF, with transistorised chassis that used the odd IC.
The following decade was one of growth. The "space race" had begun in 1957, when the USSR launched Sputnik 1 and terrified the
Americans. Thereafter the USA began to spend countless billions of
dollars on space missions. This got underway in earnest in the Sixties,
with the announcement that America would be going all out to get a man
on the moon by the end of the decade. There followed the Mercury series
of earth - orbit missions, then the Apollo launches. Success was
achieved in 1969. Most of these missions were televised, and in those
days anything to do with space was hot stuff. It was inevitable that
everyone wanted to have a television set. At the time an average
receiver would be a monochrome one with a 14in. tube - there was no
colour until 1967. It would cost about 75 guineas.
TV sets were often priced in guineas (21 shillings)
as it made the price look a bit easier on the pocket. Anyway 75 guineas,
equivalent to about £78.75 in 2000's currency, was a lot of money
then. For those who couldn't, rental was a good option. The Sixties was
a period of tremendous growth for rental TV.
Much else was rented at that time, even radios, also
washing machines, spin driers, refrigerators and, later on, audio tape
recorders (no VCRs then).
For most people these things were too expensive for cash purchase.
There were no credit cards then. And when it came to
a TV set, the question of reli- ability had to be taken into account:
renting took care of repair costs.
TV reliability.........The TV sets of the period
were notoriously unreliable. They still used valves, which meant that a
large amount of heat was generated. The dropper resistor contributed to
this: it was used mainly as a series device to reduce the mains voltage
to the level required to power the valve heaters. These were generally
connected in series, so the heater volt- ages of all the valves were
added together and the total was subtracted from the mains voltage. The
difference was the voltage across the heater section of the dropper
resistor, whose value was determined by simple application of Ohm's
Law.
As valves are voltage -operated devices, there was
no need to stabilise the current. So the power supply circuits in TV
sets were very simple. They often consisted of nothing more than a
dropper resistor, a half or biphase rectifier and a couple of smoothing
capacitors. If a TV set had a transformer and a full wave rectifier in
addition to the other components, it was sophisticated!
As the valve heaters were connected in series they
were like Christmas -tree lights: should one fail they all went out and
the TV set ceased to function. Another common problem with valves is the
cathode -to -heater short. When this fault occurs in a valve, some of
the heaters in the chain would go out and some would stay on. Those that
stayed on would glow like search- lights, often becoming damaged as a
result. Dropper failure could cause loss of HT (dead set with the
heaters glowing), or no heater supply with HT present. When the HT
rectifier valve went low emission, there was low EHT, a small picture
and poor performance all round. CRTs would go soft or low emission, the
result being a faint picture, or cathode -to -heater short-circuit, the
result this time being uncontrollable brightness. On average a TV set
would have twelve to fourteen valves, any one of which could go low
-emission or fail in some other way. All valves have a finite life, so
each one would probably have to be replaced at one time or another. The
amount of heat generated in an average TV set would dry out the
capacitors, which then failed. So you can see why people rented!
The CRT could cause various problems. Because
of its cost, it was the gen- eral practice to place its heater at the
earthy end of the chain. In this position it was less likely to be
overloaded by a heater chain fault. But during the winter months, when
the mains voltage dropped a bit, it would be starved of power. This
would eventually lead to 'cathode poi- soning' with loss of emission.
The 'cure' for this was to fit a booster transformer designed to overrun
the heater by 10, 20 or 30 per cent. It would work fine for a while,
until the CRT completely expired. At about this time CRT reactivators
came into being - and a weird and wonderful collection of devices they
turned out to be. Regunned tubes also started to appear. You couldn't do
this with the `hard -glass' triode tubes made by Emitron. These were
fitted in a number of older sets. Yes, they were still around, at least
during the early Sixties.
Developments................... A great deal
of development occurred during the Sixties. Many TV sets and radios made
in the early Sixties were still hard -wired: the introduction of the
printed circuit board changed the construction of electronic equipment
forever. The first one was in a Pam transistor radio. PCBs were ideal
for use in transistor radios, because of the small size of the
components used and the fact that such radios ran almost cold.
They were not so good for use with valve circuitry,
as the heat from the valves caused all sorts of problems. Print cracks
could develop if a board became warped. If it became carbonised there
could be serious leakage and tracking problems. In addition it was more
difficult to remove components from a PCB. Many technicians at that time
didn't like PCBs. As the Sixties progressed, transistors took over more
and more in TV sets. They first appeared in a rather random fashion,
for example in the sync separator stages in some Pye models. Then the IF
strip became transistorised. Early transistors were based on the use of
germanium, which was far from ideal.
The change to silicon produced d
evices that were more robust and had a better signal-to-noise ratio.
Car radios became fully transistorised, and
'solid-state' circuitry ceased to be based on earlier valve
arrangements. Many hi-fi amplifiers had been transistorised from the
late Fifties, and all tape recorders were now solid-state.
Both reel-to-reel and compact -cassette recorders
were available at this time. Initially, audio cassette recorders had a
maximum upper frequency response of only about 9kHz.
To increase it meant either a smaller head gap or a
faster speed. Philips, which developed the compact audio cassette and
holds the patents for the design (which we still use in 2000!) wouldn't
allow an increase in speed. Good reel-to-reel recorders had a fre-
quency response that extended to 20kHz when the tape speed was
15in./sec.
This is true hi-fi. In time the frequency response
of compact -cassette recorders did improve, because of the use of better
head materials with a smaller gap.
This led to the demise of the reel-to-reel audio
recorder as a domestic product We began to benefit from spin-offs of the
space race between the USA and the USSR.
The need to squeeze as much technology as possible
into the early computers in the Mercury space capsules used by the USA
lead to the first inte- grated circuits.
This technology soon found its way into consumer
equipment. Often these devices were hybrid encap- sulations rather than
true chips, but they did improve reliability and saved space. The few
chips around in those days were analogue devices. To start with most
UHF tuners used valves such as the PC86 and PC88. They were all manually
tuned. Some had slow-motion drives and others had push -buttons. They
didn't have a lot of gain, so it was important to have an adequate
aerial and use low -loss cable..............................
The
pilot control device which may be employed singly or may comprise three
units or their equivalent when applied to multiphase supply systems
comprises a pair of closed magnetic circuits or cores constructed of
strip wound magnetic material or stacked laminations, the two
