TV Electronics VL-100. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Portable TV "Electronics VL-100" is designed to receive television programs both at home and on the street, outside the city, in a car on a retractable telescopic antenna. His kinescope has a screen with a diagonal size of 16 cm and an electron beam deflection at an angle of 70 °. The TV is powered from a 127/220 V AC mains or from a 12 V DC source. The TV has jacks for connecting an external antenna reduction cable, headphones, a tape recorder and an additional bass amplifier. The technical characteristics of the TV are summarized in Table. 1.

Table 2

Image size	100x125 mm
Horizontal clarity	450 lines
Sensitivity for image and sound channels	100 uV
Selectivity on adjacent channels is not worse	26 dB
Rated sound power	150 MW
Battery Power Consumption	5 watts
TV dimensions	145X170X200 mm
Weight (without AC adapter)	2,8 kg

The scheme of the TV is shown in fig. 1

A 12-channel modernized PTK-P block is installed at the TV input. It differs from the PTK-P block described in "Radio", 1966, No. 1, p. 21, by the circuit for switching on the transistor of the RF amplification stage. The AGC control voltage is applied to the base of the transistor of this stage and, as the signal at the input of the TV increases, it shifts its operating point towards saturation.

The TV uses a relatively simple and easily adjustable three-stage IF image amplifier, at the input of which a five-loop lumped selection filter (FSS) is included. The first and second stages of the IF amplifier, assembled on transistors T1, T2, are loaded with single circuits, have a wide bandwidth and are covered by AGC. Carrier rejection of the audio IF (31,5 MHz) is carried out using the L10C15 circuit included in the base circuit of the T3 transistor.

The third stage of the amplifier (transistor T3) is loaded with a bandpass filter L11C18, L12C21 with external capacitive coupling through capacitor C19. This filter, together with the FSS, provides the necessary selectivity and shape of the frequency response.

Neutralization of internal feedback in the transistors of the first two stages is carried out by applying voltage from the coupling coils L7 and L9 to the bases of transistors T1i and T2 through capacitors C7 and C11. The neutralization voltage in the third stage is removed from the resistor R20 and fed to the base of the transistor T3 through the capacitor C16.

The IF image amplifier has a maximum gain of about 70 dB. The selected circuit provides a sufficiently wide bandwidth and a satisfactory phase response.

The video detector of the TV is assembled on the diode D1 according to the standard scheme. The load of the video detector is resistor R22. A U-shaped filter S22Dr1S23 is installed at the output of the video detector. The inductor of this filter is simultaneously designed to correct the frequency response of the video amplifier.

From the video detector, the signal goes to the first stage of the video amplifier, assembled on the T4 transistor according to the emitter follower circuit to match the high output impedance of the video detector with the low input impedance of the video amplifier.

Between the first and second stages of the video amplifier, the L13C25 rejector circuit is connected, tuned to a frequency of 6,5 MHz, from which the audio signals are taken to the IF amplifier. The second stage of the video amplifier is made on a T5 transistor, connected according to a common emitter circuit and a complex frequency response correction. From the video amplifier, positive polarity signals are fed to the cathode of the kinescope, the AGC device and the selector of the synchronization unit. Direct DC connection between the load of the video detector and the kinescope cathode ensures the transmission of the DC component of the video signal. The image contrast is adjusted by changing the voltage of the video signal at the cathode of the kinescope using the R35 potentiometer. The frequency response distortions that appear with this contrast adjustment method are compensated using capacitors C30 and C31. The video amplifier has a gain of at least 70 with a bandwidth of 4,75-5 MHz.

The AGC device contains two stages: a key stage on a T6 transistor and a DC amplifier on a T7 transistor. A negative delay voltage of 6-5 V is applied to the base of transistor T6. It will open only if the level of the signal taken from the video amplifier exceeds the threshold value of the delay, and at the same time, positive reverse pulses from the output to the output horizontal scanning transformer, coinciding in frequency and phase with sync pulses, arrive at the collector of this transistor. Transistor T7 of the DC amplifier is connected according to a common emitter circuit. It is connected to the key stage through a two-section filter C35 R45 and C36 R47, which determines the AGC time constant. In the absence of a signal or with a weak signal, the transistor T7 is closed and does not cause a change in voltage, and therefore, in the current in the AGC circuits. When the signal exceeds the delay threshold, this transistor, like T6, opens and a positive AGC control voltage appears at the output of the cascade.

The TV sound channel consists of two resonant stages of the IF sound amplifier on transistors T8 and T9, included in a common emitter circuit, a frequency ratio detector on diodes D2, D3 and a low-frequency amplifier on transistors T10-T12.

To obtain maximum IF gain, the load circuits L15C40 and L17C43 are completely included in the collector circuits of transistors T8, T9. Resistors R49, R53, R56, R58 serve to prevent self-excitation of the IF amplifier. The relationship detector is assembled according to a symmetrical scheme. Such a detector is easier to set up and better suppresses parasitic amplitude modulation. The LF amplifier has no features. Its output power is 150 mW. It is loaded with two loudspeakers 0,1GD6.

The synchronization unit consists of three stages: an amplitude selector (transistor T21), a phase inverter (T22) and a frame sync buffer amplifier (T13). From the amplitude selector, the horizontal sync pulses after differentiation enter the phase inverter, at the outputs of which horizontal sync pulses of both polarities with an amplitude of about 5 V are emitted. These pulses enter the AFC and F system, assembled on diodes D4, D5. The vertical sync pulses are separated from the horizontal ones in a two-section integrating filter R101C62, R100C61 and amplified in the buffer stage. From the output of this cascade, clock signals in negative polarity are fed to a vertical scanning master oscillator.

The line scan unit consists of three stages: a master oscillator on a transistor T23, a preliminary amplification stage (T24) and an output stage (T25). The line-scan master oscillator is made according to the scheme of a blocking oscillator with an emitter-base coupling. Such a generator has a high input impedance, which is necessary for the normal operation of the AFC and F. Sawtooth pulses are taken from the connection point of the load resistors R113 and R114 in the collector circuit of the T23 transistor. Due to this connection to the generator of the preliminary amplification stage, the influence of its changing input resistance on the operation of the blocking generator is excluded. The duration of the sawtooth pulses is largely determined by the resistances of the resistors R11, R113 and R114. The frequency of pulses also depends on the last two.

The preliminary amplification stage of the horizontal scanner (T24) operates in key mode and performs the functions of a power amplifier. Transistor T24 has a conductivity that is the opposite of the conductivity of transistor T23. During the forward sweep stroke, this transistor is closed. It opens with pulses of positive polarity coming from the blocking generator. Further, through a matching transformer Tr4, a pulse signal without a constant component enters the base of the transistor T25 of the horizontal scanning output stage. This cascade operates in the double-sided key mode and is loaded with an output horizontal transformer, to which the horizontal coils of the deflecting system are directly connected. To pass the constant component of the collector current, the T25 transistor is connected to a power source through the winding of a horizontal transformer.

During the forward stroke of the horizontal scan, the transistor T25 is in saturation and is able to pass a large current through the output horizontal transformer Tr5 and the deflecting horizontal coils. At the beginning of the reverse stroke, a positive rectangular pulse with a short rising edge time is applied to the base of the transistor through a matching transformer, which quickly turns off the transistor. The positive voltage pulse that occurs in the horizontal transformer during the reverse path of the beam is used to obtain the supply voltage of the second anode of the kinescope (9 kV), the accelerating and focusing electrodes (500 V), the kinescope filament voltage (1,35 V), the power supply of the transistor T5 ( 80 c) and other auxiliary voltages. Diode D6 is used as a damper.

The vertical scanning unit is made according to a transformerless scheme. The master oscillator is assembled on transistors T14, T15, T16 according to the multivibrator circuit with emitter coupling. In this cascade, a combination of a linearly varying voltage generator with a non-linear resistance (transistor T16) and a relaxation generator (transistors T14 and T15) is implemented. The swing of the sawtooth voltage at the output of the master oscillator is almost equal to the supply voltage.

A push-pull class "B" power amplifier on two composite transistors (T17-T19 and T18-T20) was used as a vertical scan output stage. The non-linear distortion of the "step" type, characteristic of the "D" class, is eliminated by selecting the bias voltage at the bases of the transistors.

The TV "Electronics VL-100" is powered from the AC mains through a stabilized rectifier with an output voltage of +10,5 V relative to the TV case. The remote power unit consists of a small-sized power transformer (Tr6), a rectifier bridge (D14 - D17) and a filter capacitor (C95). To stabilize the raster size and parameters of the TV when operating from a DC voltage source or a car generator, the voltage regulator is structurally placed directly in the TV case. It is made on a transistor T26 (control stage), T27 (pass stage) and a reference diode D13. A negative voltage of 131 V is supplied to the stabilizer through the divider R134-R12 from a special rectifier D80S50, which is generated in the line scanner. This voltage sets the operating mode for the regulating transistor T26. A feature of the stabilizer is the dependence of the operating mode of the pass transistor T27 on the voltage - 50 V supplied to the base of the transistor T26. This allows you to protect the T25 transistor, the horizontal scan output stage, and the T27 transistor from breakdown. The stabilizer keeps the output voltage of the rectifier constant when the mains voltage changes within ±10%. It has a ripple factor of not more than 100 mV. The rectifier circuit provides pads for charging a 12-volt portable battery. The battery can be charged while watching TV.

Structurally, the TV "Electronics VL-100" consists of several functional blocks. Two main printed circuit boards - the receiver board and the scanning board - are located vertically on both sides of the kinescope, and the third board with auxiliary rectifiers and the PTK-P block is on top. All three boards are hinged and attached to the carrier frame with hinges. The TV has an easily removable metal case, which, when removed, provides access to the entire installation. A handle with a built-in telescopic articulated antenna is fixed on the top wall of the case. The kinescope screen occupies the entire area of ​​the front panel. Loudspeakers 0,1GD6 are located at the bottom of the TV in a horn speaker system.

The winding data of the contour coils of the TV are summarized in Table. 2, and transformers - in table. 3.

Table 2

Scheme designation	Number of turns	Wire: brand and diameter, fox
L1	25	PELSHO 0,2
L2	10	"
L3	15	"
L4	35	"
L5	25	"
L6	15	"
L7	5	"
L8	15	"
L9	5	"
L10	35	"
L11	20	PELSHO 0,35
L12	20	"
L13	15	PELSHO 0.2
L14	10	"
L15	31	"
L16	6	"
L17	35	PELSHO 0.1
L18	18x2	LESHO 7x0.07
L19	15	PELSHO 0.1
L20	650	PEV 0,13

All coils are wound on frames with a diameter of 6 mm in one layer (excluding L20), turn to turn (L17 and L19 on one frame, L18 - in two wires), and tuned with tuning cores SB-12a (SB-1a), with the exception of L20 , for which a ferrite core of the KNF-13 type is used.

Table 3

designation	Core	NN pins	Number of turns	Wire: brand and diameter, mm
Tr1	Permalloy 45N Sh4x5	1-2 3-4 4-5	2100 290 290	PEV-1 0,06 PEV-1 0,06 PEV-1 0.06
Tr2	Also	1-2 3-4 4-5	450 450 80	PEV-1 0,09 PEV-1 0,09 PEV-1 0,23
Tr3	Oksifer M1500NM type B14	1-2 3-4	500 100	PEV-1 0,08 PEV-1 0,08
Tr4	Also	1-2 3-4	250 50	PEV-1 0,08 PEV-1 0,23
Tr5	Oksifer M2000NM Sh 7x7	1-3 3-2 2-6 6-4 4-5 5-7	25 5 10 36 600 2700	PEV-2 0,15 PEV-2 0,35 PEV-2 0,35 PEV-2 0,35 PEV-2 0,05 PEV-2 0,05
Tr6	Steel 3310 ShL 12X20	1-2 2-3 4-5	1607 1160 175	PEV-1 0,22 PEV-1 0,15 PEV-1 0,64
DR1	Oksifer M1500NM type B14		120	PEV-2 0,12
Dr2	Ferrite 600NN length 40 mm, diameter 4 mm (from RLS-70)		60	PEV-2 0,23

Authors: L.Kisin, G.Sadovskaya, V.Uteshev; Publication: N. Bolshakov, rf.atnn.ru

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