CONIC TV-FM/AM RADIO TR-7200 YEAR 1979.

The CONIC TV-FM/AM RADIO TR-7200  is A Hand Portable B/W Telly with incorporated radio receiver.

It has manual tuning for Both VHF and UHF channels and for FM and AM radio frequency and incorporated antenna for both features..

The CONIC TV-FM/AM RADIO TR-7200 is a television receiver which is capable of receiving not only television signals, but also broadcast FM /AM radio signals. In the United States, the broadcast FM band occupies a band of frequencies extending from approximately 88 MHz to approximately 108 MHz. This band of frequencies lies between the frequencies allocated for broadcast television channel 6 and television cable channel 98. Modern intercarrier sound-type television receivers having the capability to receive broadcast FM signals are known from the prior art. However, in these known arrangements, their respective manufacturers added a separate FM radio having its own tuner. This may have been done because television tuners commonly include tuned circuits (FM traps) for trapping out FM signals which may otherwise interfere with television signal reception. A typical FM trap for a television receiver is a tuned circuit exhibiting an amplitude vs. frequency characteristic having a single deep notch substantially centered on the FM band of frequencies, and sufficiently wide to attenuate FM signals throughout the FM band of frequencies. Not surprisingly, removing the FM trap degrades the performance of the receiver when tuning television signals.

 Such receivers are provided with a tuner for selecting the different emitter frequencies of the radio and television station signals. These antenna signals fed to the tuner are transformed in the tuner by mixing with an oscillator frequency to an intermediate frequency. The intermediate frequency signals taken from the tuner are amplified in a following intermediate frequency amplifier. A demodulator following to the intermediate frequency amplifier demodulates the high frequency modulated signal to an audio frequency sound signal or respectively to a video frequency picture signal, which is fed to the final stages for reproduction in a loudspeaker or respectively on the screen of a television set. The individual electronic components such as tuner, intermediate frequency amplifier and demodulator have been conventionally disposed in separate component parts and were connected to each other via lines.


It has a typical conventional indicator driving device for a television receiver incorporating a radio receiver includes a TV channel selecting pulley, a radio frequency selecting pulley, two drums spaced from each other and between which is stretched a frequency indicator sheet, a drive shaft and a manipulating knob fixed to the drive shaft. The torque imparted to the drive shaft is transmitted from the latter to the above-mentioned two pulleys and two drums through wires thereby driving the indicator. Thus, the conventional indicator driving device has a complicated structure because of the use of the frequency indicator sheet which inevitably necessitates two drums. In addition, the conventional indicator driving device has a drawback in that the matching between the tuner of the radio receiver and the frequency indicator sheet is rather difficult to obtain.

It's very light weight compared to others types.

It can powered from mains and battery pack fitted on the floor box under the telly itself.

It seems the first model maketed from Brand name CONIC in 1979-1980, see descriptions below.

Conic Electronic Industries

New delhi, Delhi, India

Telecommunication Products - Manufacturer, Export / Import,
Proprietorship Firm Since 1980

In 1977, Mr. Maini realized the growing potential of the electronics industry in India and he started a small electronic products manufacturing firm called CONIC ELECTRONIC INDUSTRIES.

Through his hard-work and strong vision, he soon transformed this small firm into one of the most successful brand names making a variety of audio and video products. Today, his innovative ideas have enabled Conic achieve the First mover advantage in many of its products and has helped keeping the company ahead of the market at all times.

With the support of his wife Mrs. Preeti Maini, he has come out to be a true leader in all spheres of life. He enabled Conic to become one of the best professionally managed companies. The electronic industries federation recognized his qualities as a leader and rewarded him with the prestigious "SPIRIT OF INDIA" award.

MANUFACTURER AND EXPORTER OF PRODUCTS AS DVD/ VCD/ MP3 PLAYER, DTH SATELLIT RCVR, TV, PORTABLE DVD PLAYER, HOME THEATRE, SPEAKERS, STEREO DECK. Our products of DVD Player VCD Player Home Theater Satellite Receiver Stereo System Speaker System.

(NOTE: I know they were even manufactures of electronic calculators and hand electronic games because I have some of these lying around here in my stuff.)

The brand seems now DEFUNCT.

CONIC TV-FM/AM RADIO TR-7200 CHASSIS 72C080 INTERNAL VIEW.

The chassis of the CONIC TV-FM/AM RADIO TR-7200 is mainly divided by sections:

-Power supply on bottom floor / battery compartment (contains even the AUDIO IC Amplifier).

- Television chassis right side (photographed front)

- Radio chassis on the front of the apparatus itself

- Speaker on the rear side lid.

The chipset of ASIC'S used in this chassis are:

HA11229
TBA810P
LA1210

CONIC TV-FM/AM RADIO TR-7200  CHASSIS 72C080 Indicator driving device for television receiver incorporating radio receiver:

 The CONIC TV-FM/AM RADIO TR-7200 is a television receiver which is capable of receiving not only television signals, but also broadcast FM /AM radio signals.

 An improvement in the indicator driving device for use in a television receiver incorporating a radio receiver is shown. There is provided an indicator driving device of a type in which the selection of a channel for the television receiver and the selection of a frequency for the radio receiver are performed by means of a common manipulating knob. The improvement resides in a much simplified construction and facilitation of work for obtaining synchronization or matching between the frequency selecting variable capacitor of the radio receiver and the frequency indicator.

 1. An indicator driving device for a television receiver incorporating a radio receiver, comprising: an indicator drum rotatably supported at one end by a bracket, said indicator drum having a plurality of numerals printed on its outer peripheral surface and representing the numbers of channels for said television receiver and the frequencies for said radio receiver; a channel selecting potentiometer attached to said bracket and having a rotary shaft directly coupled to the other end of said indicator drum thereby supporting said indicator drum; a manipulating knob rotatably mounted on said bracket and carried by a drive shaft one end of which constitutes a wire winding drum portion; a frequency selecting pulley connected to the rotary shaft of the frequency selecting means of said radio receiver; an intermediate gear meshing with a gear formed on one end of said indicator drum; an intermediate pulley connected to said intermediate gear and rotatably supported by said bracket; a driving wire wound round said wire winding drum portion of said drive shaft, said intermediate pulley and said frequency selecting pulley; and means associated with said frequency selecting pulley for imparting tension to said driving wire.

2. An indicator driving device as claimed in claim 1, characterized in that said intermediate gear and said intermediate pulley are rigidly connected to each other by means of at least one screw, said screw being adapted, when loosened, to permit said intermediate gear and said intermediate drum to rotate freely and independently of each other.

Description:

BACKGROUND OF THE INVENTION
The present invention relates to a frequency indicator driving device of a television receiver having an electronic tuner and incorporating a radio receiver and, more particularly, to an improvement in the indicator driving device capable of performing the selection of TV channels and the selection of radio frequencies by only one manipulating knob.
A typical conventional indicator driving device for a television receiver incorporating a radio receiver includes a TV channel selecting pulley, a radio frequency selecting pulley, two drums spaced from each other and between which is stretched a frequency indicator sheet, a drive shaft and a manipulating knob fixed to the drive shaft. The torque imparted to the drive shaft is transmitted from the latter to the above-mentioned two pulleys and two drums through wires thereby driving the indicator. Thus, the conventional indicator driving device has a complicated structure because of the use of the frequency indicator sheet which inevitably necessitates two drums. In addition, the conventional indicator driving device has a drawback in that the matching between the tuner of the radio receiver and the frequency indicator sheet is rather difficult to obtain.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to simplify, in a television receiver having an electronic tuner and incorporating a radio receiver, the construction of the indicator driving device of the type having a single manipulating knob for selecting operations of both the radio receiver and the television receiver.
It is another object of the invention to facilitate the adjustment, synchronization or matching between the frequency selected by the radio receiver and the frequency indicated by the frequency indicator.
To these ends, according to the invention, there is provided a frequency indicator driving device for a television receiver having an electronic tuner and incorporating a radio receiver, comprising an indicator drum on the periphery of which are marked the numerals representing the codes of television broadcasting stations and the radio frequencies, the indicator drum being directly connected at its one end to the shaft of a channel selecting potentiometer of the television receiver so as to be supported by the shaft; a gear fixed to the other end of the indicator drum and meshing with an intermediate gear; an intermediate pulley fixed to the intermediate gear by means of screws; a frequency selecting pulley coupled to the shaft of a variable capacitor constituting the tuner of the radio receiver; a drive shaft to which a manipulating knob is fixed; and a driving wire wound round the intermediate pulley and the frequency selecting pulley via the drive shaft.
These and other objects, as well as advantageous features of the invention will become more clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a conventional indicator driving device;
FIG. 2 is a right side elevational view of the device shown in FIG. 1;
FIG. 3 is a front elevational view of an indicator driving device constructed in accordance with a first embodiment of the invention;
FIG. 4 is a sectional view taken along the line IV--IV of FIG. 3;
FIG. 5 is a right side elevational view of the device shown in FIG. 4;
FIG. 6 is a top plan view of the device shown in FIG. 4;
FIG. 7 is a right side elevational view of the device shown in FIG. 4;
FIG. 8 is a sectional view taken along the line VIII--VIII of FIG. 7;
FIG. 9 is a sectional view taken along the line IX--IX of FIG. 7;
FIG. 10 is a sectional view taken along the line X--X of FIG. 4; and
FIG. 11 is a left side elevational view of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before turning to the description of the preferred embodiments, a description will be made hereinunder as to the conventional frequency indicator driving device for a television receiver incorporating a radio receiver, in order to clarify the drawback of the prior art and, hence, the advantages of the invention.
Referring first to FIGS. 1 and 2 showing a typical conventional device of the kind described, a drive shaft 1 is rotatably attached to a bracket 3 by means of a U-shaped fitting 2. The drive shaft 1 has a knurled end portion 4 which is fitted to a bore formed in a manipulating knob 5. Drums 8, 9 to one ends of which attached are pulleys 6, 7 are rotatably received at their one ends by a bore 10 and at their other ends by means of the notches 11, 12. In order to rotatably drive a channel selecting pulley 13 and a frequency selecting pulley 14, a wire 16 is wound by several turns round each of a winding drum portion 15 of the drive shaft 1, and pulleys 6, 7. The wire 16 is further wound round the channel selecting pulley 13 and the frequency selecting pulley 14. A spring 17 is provided to pull and fix the wire 16.
In the described arrangement, therefore, the pulleys 13, 14 are rotated in synchronization with each other as the manipulating knob 5 fitted to the drive shaft 1 is rotated, thereby simultaneously selecting both the television channel and the radio frequency. Further the frequency indicating sheet 18 wound round the selecting drums 8, 9 is driven thereby displaying the frequency. In FIG. 1, a reference numeral 19 denotes a spring adapted to rotatively bias the selecting drum 9 so as to impart a tension to the frequency indicating sheet 18, while reference numerals 20, 21 designate rollers.
It will be seen that this conventional indicator driving device has a complicated construction due to the use of the frequency indicating sheet which inevitably necessitates two drums.
Under these circumstances, the present invention aims at providing an indicator driving device in which the tuning operations for the radio receiver and the tuning operation for a television receiver are made through a common manipulating knob by an improved and much simplified mechanism.

A preferred embodiment of the invention will be described hereinunder with reference to FIGS. 3 to 11. In the indicator driving device of the invention, an indicator drum, on the peripheral surface of which are marked numerals representing the frequencies is used in place of the frequency indicating sheet of the conventional frequency indicating device. The shaft of the channel selecting volume is directly connected to the frequency indicator drum. An indicator gear is unitarily attached to the frequency indicating drum. The indicator gear is arranged to mesh with an intermediate gear to which coaxially attached is an intermediate pulley. A driving wire wound round the intermediate pulley is wound round and stretched between a drive shaft and the frequency selecting pulley and is pulled and fixed by means of a spring.

Referring to the drawings, a bracket 30 is fixed by means of a plurality of screws 31 to a front cabinet 32, as will be most clearly understood from FIG. 5. A reference numeral 33 denotes a printed circuit board on which are formed the major part of the radio receiver circuit, while a variable capacitor for selecting a frequency for the radio receiver is designated at a reference numeral 34. As will be clearly seen from FIGS. 5 and 10, the variable capacitor 34 is fixed to the printed circuit board 33. A frequency selecting pulley 35 is fixed by means of a screw 36 to the rotary shaft of the frequency selecting variable capacitor 34.
An intermediate gear 37 has, as detailed in FIG. 8, a journal portion which is rotatably received by a bore 38 formed in the bracket 30. A reference numeral 39 denotes an intermediate pulley having a cylindrical portion inserted into the bore 38 of the bracket 30 in the opposite direction to the inserting direction of the intermediate gear 37. The journal portion of the intermediate gear 37 is fitted to the inside of the cylindrical portion of the intermediate gear 37 and is fixed to the latter by means of a small screw 40, as will be clearly seen from FIG. 8.
A reference numerals 41 denotes an indicator drum on the outer peripheral surface of which are printed numerals representing the television channels and the numerals representing the radio frequencies in side-by-side relation. An indicator gear 43 is fixed to the open end of the indicator drum 41, as shown in FIG. 7.






Referring now to FIG. 10 showing the detail of construction of the indicator driving device, a boss 44 formed integrally with the indicator gear 43 is rotatably received by a bore 45 formed in the bracket 30. A channel selecting potentiometer 48 is fixed to a potentiometer fixture 46 by means of a nut 47 and a washer. The potentiometer 48 has a rotary shaft 49 which extends through a bore 50 formed in the other end of the bracket 30. The rotary shaft 49 is press-fitted into a bore 51 formed in the other end of the indicator drum 41 coaxially with the boss 44. This potentiometer fixture 46 is fixed to the bracket 30 by means of a bolt 52.
Therefore, the rotary shaft 49 of the channel selecting potentiometer 48 is rotated following the rotation of the indicator drum 41. In other words, the indicator drum 41 is supported at its other end by a rotary shaft 49 of the channel selecting potentiometer 48.
In fixing the rotary shaft 49 to the indicator drum 41, it is necessary to select the angular positional relationship between these two members such that a standard channel is selected when the potentiometer 48 has been fully rotated in one direction and that the number of the selected channel on the indicator drum is aligned with the pointer or hand which will be described later.
As shown in FIG. 7, the indicator gear 43 meshes with the intermediate gear 37 when the boss 44 of the indicator gear 43 is fitted to the bore 45. A manipulating wheel 53 is received by a recess 54 formed in the bracket 30 such that a portion thereof is exposed to the outside of the front cabinet 32 as will be most clearly seen from FIG. 10. The manipulating wheel 53 is so positioned that a central bore thereof is aligned with the bore formed in the bracket 30. A drive shaft 55 has one end constituting a wire winding drum portion formed unitarily therewith and the other end which is extended through the aforementioned bore of the bracket 30 and fixedly received by the central bore of the manipulating wheel 53 so as to support the latter for unitary rotation with the drive shaft 55. A reference numeral 56 denotes an E-shaped ring or retainer fixed to the other end of the drive shaft to prevent the latter from being disengaged.
A reference numeral 57 denotes a driving wire which is wound round the wire winding drum portion of the drive shaft 55 by several turns, and then round the intermediate pulley 39. The wire runs around a roller 58 and is further wound round the frequency selecting pulley 35. The wire is then connected at its one end to one end of a spring 59 which in turn is connected at its other end to the frequency selecting pulley 35, so as to be held and tightened by the spring 59. Therefore, the pulleys 35, 39 are rotated as the driving rope 57 is moved.
A reference numeral 60 denotes change-over or selection push buttons such as for switching between the VHF and UHF channels of a television receiver, between the AM and FM bands of the radio receiver and a weather band WB for receiving weather forcasts. A reference numeral 61 denotes a contrast adjusting knob, while a brightness control knob is designated at a reference numeral 62. A knob denoted by a reference numeral 63 is provided to play the double role of power switch and a volume control knob. A reference numeral 64 denotes a push button for turning on and off a lamp 65 for illuminating the indicator drum 41. A reference numeral 66 denotes an indicator cover plate which is originally transparent and formed to correspond to the indicator drum 66. The indicator cover plate 66 is provided with a linear pointer or reference line 67. The portion of the indicator cover plate 66 other than the portion around the reference line 67 is made opaque in the finished state of the indicator cover plate 66. A reference numeral 68 denotes an earphone socket fixed to the front cabinet, while a reference numeral 69 designates a lower cabinet. Reference numerals 70 and 71 denote, respectively, a bar antenna for the radio receiver and a retainer for the bar antenna. Reference numerals 72 and 73 denote potentiometers and reference numeral 74 a combined potentiometer and switch corresponding to the aforementioned knobs 61, 62 and 63.
The potentiometer 72, 73 and the combined potentiometer and switch 74 are fixed to a second bracket 75 which is fixed to the front cabinet 32 by means of screws 76. A reference numeral 77 designates a printed circuit board constituting the circuit of the tuner for the television receiver. A VHF tuner 78 and a UHF tuner 79 for the television receiver are fixed to the printed circuit board 77.
A reference numeral 80 denotes switches corresonding to respective change-over buttons 60. A roller pin for rotatably supporting the roller 58 is designated at a reference numeral 81. Finally, a reference numeral 82 denotes a volume for fine adjustment of the tuning voltage.
In operation, assuming here that the manipulation knob 53 is rotated to select the desired channel after depression of the change-over button 60, the driving wire 57 is pulled to rotate the indicator drum 41 through the action of the intermediate pulley 39, the intermediate gear 37 and the indicator gear 43. Meanwhile, the rotary shaft 49 of the channel selecting potentiometer 48 for the television receiver is rotated to select the desired channel. Simultaneously, the number of the selected channel is indicated by cooperation of the numeral 42 marked on the indicator drum 41 and the reference line 67 of the indicator cover panel 66.
Heedless to say, the frequency selecting pulley 35 is also rotated. Thus, if the push button 60 for FM radio frequency operation has been depressed, the radio receiver operates to select the FM radio frequency through the action of the frequency selecting pulley 35 and the frequency selecting variable capacitor. It will be clear to those skilled in the art that, in this state of the radio receiver, the numerals 42 marked on the indicator drum 41 and the reference line 67 on the indicator cover cooperate with each other to indicate the received frequency.
It will be seen that the construction is greatly simplified as compared with the aforementioned conventional device. This is entirely due to the use of the indicator drum 41 to which is directly connected a channel selecting potentiometer 48. Namely, simplification of the construction has been achieved by making the indicator drum 41 take part in the power transmission and by supporting one end of the indicator drum 41 by the rotary shaft 49 of the potentiometer 48.
Hereinafter, a description will be provided to show how matching between the variable capacitor 34 of the radio receiver and the positions of numerals on the indicator drum 41 is attained.

To this end, at first the screw 40 for fixing the intermediate gear 37 to the intermediate pulley 39 is loosened to permit the intermediate gear 37 and the intermediate pulley 39 to rotate freely relative to each other. Then, the frequency selecting variable capacitor 34 is rotated fully to the minimal position, the indicator drum being rotated to make the starting point of the legend 42 coincide with the reference line 67. The screw 40 is then tightened to rigidly connect the intermediate gear 37 and the intermediate pulley 39 to each other. To make this adjustment, the screw 40 is left not tightened in the assembling process of the driving device, and the above-stated adjustment is made after stretching the driving wire 57.
As has been described, according to the invention, an indicator drum having numerals marked thereon to represent the number of channels for the television receiver and the frequencies for the radio receiver is used in place of the frequency indicating sheet employed in the conventional device. The rotary shaft of the channel selecting potentiometer is directly coupled to one end of the indicator drum to support the latter, while a gear attached to the other end of the indicator drum is made to engage an intermediate gear to which is fixed an intermediate pulley. Further, a frequency selecting pulley is coupled to the rotary shaft of the frequency selecting variable capacitor. The driving wire is wound round the drum portion of the drive shaft to which the manipulating knob is fixed, and is also wound round the intermediate pulley and the frequency selecting pulley.
This arrangement offers two advantages: a highly simplified construction of the indicator driving device and a facilitation of the work for obtaining matching between the variable capacitor of the radio receiver and the indicator drum.

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 disclosed 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.