GE-802-Rider-TV-1电路原理图.pdf

TV PAGE 1-52 GE MODEL 802 GENERAL ELECTRIC CO. VIDEO R-F VIDEO .f. VIDEO AMPLIFIER SPEAKER rig. 1. Block Diagram, Model 802 GENERAL INFORMATION The General Electric Model 802 television receiver is a con- sole type, 26-tube instrument providing reception of all 13 commercial television channels, radio reception in the Broadcast and FM bands, and phonograph reproduction using the new G-E Variable Reluctance Pickup. The television picture is reproduced on a 10-inch electromagnetically deflected picture tube. Tne phonograph makes use of an automatic record changer that will handle up to ten 12-inch records or twelve 10-inch records. All electrical components are mounted on a single chassis, permitting optimum ease in adjustment and service. Features of the television receiver include a constant input impedance r-f amplifier, ion trap, safe high voltage power supply, automatic frequency control for horizontal synchronization, ten- inch picture tube, and high fidelity FM audio system. On late production receivers, a Type 10FP4 picture tube is used. This makes use of metallic film on the screen which does not require the use of an ion trap. DESCRIPTIONTELEVISION AND RADIO CIRCUITS The receiver circuits are divided into the following sections: 1. R-F amplifier, converter and oscillator. 2. Video and audio i-f amplifier. 3. Video detector and amplifier. 4. Sync pulse clipper-amplifier. 5. Horizontal multivibrator and AFC sync. 6. Horizontal sweep output. 7. Vertical multivibrator and sweep output. 8. High voltage power supply (H.V. supply). 9. Low voltage power supply (L.V. supply). A brief description of the operation of each section is described in the following paragraphs. This will be supplemented by a com- prehensive television training course in the publication, RSM-4- TV. A block diagram of the complete receiver is shown in Figure 1 .to assist in signal tracing and to better visualize the operation of the receiver as a whole. I. R-f AMPLIFIER, CONVfKTfR AND OSCILLA7OK (SEE FIGURES 2 AND 3).The television and FM r-f amplifier makes use of a Type 6AU6 tube connected as a triode grounded-grid amplifier. The antenna is connected into the cathode circuit so as to pro- vide a substantially constant input impedance of 300 ohms to the antenna at all frequencies. With a 300-ohm antenna and Fig. 2. Television and F-M R-F Amplifier, Converter and Oscillator L34 9-C ) I-F CHOKE f C63jfWAVE TRAP TUNING CORE Fig. 3. Broadcast Converter and Oscillator John F. Rider RadioFans.CN GE TV PAGE 1-53 GENERAL ELECTRIC CO.MODEL 802 transmission line system, this coupling arrangement permits optimum transfer of signal from antenna to r-f amplifier for all 13 channels and also prevents reflections from being set up on the transmission line. R2 is the normal bias resistor. A choke, Lk, is placed in series with this cathode resistor to prevent the input impedance from being lowered by the shunting effect of the total stray capacity to ground of the cathode of the tube. The choke value is changed for different channels. For television operation, the r-f amplifier is coupled to the converter tube by a wide band transformer consisting of wind- ings L, and Ls. The windings are overcoupled and self-tuned by the distributed and tube capacities to provide optimum gain and band width. On channels No. 1 and No. 2, the transformer is triple tuned to prevent the image frequencies of the 88 to 108 me FM band from interfering with these two channels. For FM reception in the 88-108 me band, the r-f amplifier is coupled to the converter through the Guillotine Tuner Unit, L9. This unit operates as an auto-transformer, the inductarice, and therefore frequency, of which is varied by the tuning vane which travels in and out of L9. L9 is tuned to resonance by the stray and tube capacities, as well as by a trimmer, C8. The triode converter is one section of a Type 7F8 dual triode, V2. Bias for this tube section is provided by the oscillator voltage appearing in the grid of the converter tube, causing grid rectifica- tion charging the grid resistor-condenser combination, R3 and C9. The oscillator makes use of the remaining half of the Type 7F8 tube, V2B, and for television operation, the oscillator voltage is coupled inductively to the converter grid by locating the oscillator grid coil, Losc, adjacent to the converter grid coil, Ls. For FM operation, the oscillator voltage is coupled through capacitor C53 into the grid circuit tuning circuit, L9. The oscil- lator is a modified Colpits oscillator, oscillation being produced by the cathode-to-grid, CK, and cathode-to-plate, Ck, interelec- trode capacities of the oscillator tube. C105 shunts CB to provide uniform operation. The choke, L20, provides a d-c ground to the cathode of the oscillator tube but maintains the cathode off- ground at the r-f frequencies. The oscillator operates on the high frequency side of the r-f signal on all bands. For broadcast reception, no r-f amplifier stage is used, the r-f signal being applied directly to a Type 6BE6 mixer, V26. Here the broadcast signal is converted to 455 kc in the plate circuit. The oscillator section of V2 operates as the local oscillator for broadcast, operating on the high frequency side of the incoming signal. The oscillator is connected in a Hartley circuit by taking off the cathode tap on LI 8 which forms part of the grid tank circuit. The oscillator voltage is capacity coupled to mixer grid through C52. Tuning through the broadcast band is accomplished by moving powdered iron cores in the mixer and oscillator grid tank coils which are ganged to the tuning control and dial scale. The r-f unit, including the r-f amplifier, converter and oscillator tubes and their associated components, is constructed as a com- plete unit sub-assembly which can be demounted from the main chassis. 2. VIDIO-AND AUDIO I-F AMPLIFIERS (SEE FIGURE 4)The video i-f. amplifier consists of a three-stage band-pass amplifier using three Type 6AC7 tubes. The transformers, T15, T16, T17, and 18, are overcoupled and then loaded with resistance to give adequate (approx 4 me) band-pass frequency characteristic. A series tuned trap consisting of L32, C127 and C126 tuned to 27.9 me is connected in the 1st i-f amplifier grid circuit to provide rejection of the adjacent channel sound. A tertiary trap winding TO C 13 on transformers T16 and T17, tuned to 21.9 me, is used to provide rejection of the same channel audio. A series tuned 21.9 me trap is used at the diode stage (T18). The audio i-f frequency is developed by taking the 21.9 me sound i-f signal from across the trap at T16 and applying it to the 2nd converter tube, V4. At this tube, the 17.4 me local oscillator combines with the 21.9 me to form a difference fre- quency of 4.5 me. At this frequency it is amplified by V5, applied to the limiter tube V6 and then detected. Since the audio channel of the television is frequency-modulated, the transformer T24 functions with sections of V7A as the discriminator. This double conversion used to receive the 88 to 108 me FM band, provides high gain and selectivity necessary for tuning of the FM stations. A low negative voltage derived from the output damping tube (V23) grid circuit is applied to the contrast control R108A and then to the grids of the i-f amplifier tubes V3 and V12. This is used to change bias on these tubes and therefore the video i-f gain. 3. VIDEO DETECTOR AND AMPLIflER (SEE FIGURE 5)The video i-f amplifier output is applied to a diode rectifier, VISA, and the diode load, R18, is.connected so as to develop a negative- going signal at this point. The signal is amplified by the pentode amplifier, V14, and then applied to the cathode of the picture tube, V24, through the coupling capacitor C3. The remaining diode section of VIS is used to provide d-c reinsertion to the picture at the picture tube. VI4 LH C3 TO BRIGHTNESS CONTROL Fig. 4. Video and Audio I-F Amplifier Fig. 3, Video Detector and Amplifier The chokes L10 arid L14 are series-peaking chokes, while L15 is a shunt-peaking choke. These are used to obtain good high- frequency response. L10 in combination with C33 also prevents harmonics of the i-f frequency from being passed through the video amplifier. R23 is the V14 tube plate load resistor. Since the cathode of the picture tube is normally at a positive voltage, by the fact that it is returned to a B + source, a variable positive voltage is also applied to the grid of V24 for control of the brightness or beam current. As long as this grid voltage is less positive than the cathode voltage, the tube beam current will be within its rating. This positive voltage on the grid is controlled by Brilliance control potentiometer, R108B. 4. CUPPER AND SYNC AMPLIFIERThe triode section, VI6A, of a Type 6SN7GT tube is used to separate the sync pulses from the composite video signal taken off at the load resistor, R23. The clipper tube, V16A, is operated at a very low plate voltage and its bias is derived by grid rectification of the positive polarity video signal applied to the grid. Thus, conduction in V16A will occur only during the sync pulse intervals which are the most positive component of the video signal. Tube V16B is a horizontal synchronizing amplifier which operates into the AFC input transformer, T19. This transformer by virtue of its low inductance acts as an integrator; that is, in the secondary, the original sync signals become positive and negative pips. Only the pip that is representative of the leading edge of the synchronizing pulse is used. The vertical synchronizing amplifier tube, V18B, receives the sync pulse at its grid circuit through an integrating circuit con- sisting of R30 and C136. This integrating circuit accepts the wide vertical pulses and further amplifies them while the horizontal pulses do not have sufficient energy to charge the integrating circuits and are, therefore, attenuated. The tube V18B is operated as a cathode follower and further integration of the sync signal is provided in its cathode circuit. 5. HORIZONTAL MULTIVIBRATOR AND AFC SYNC (SEE FIGURE 6)The horizontal sawtooth oscillator makes use of a Type 6SN7GT tube, V21, in a conventional cathode-coupled multi- vibrator circuit. Instead of its frequency being controlled directly by the horizontal sync pulses, it is controlled by a d-c voltage on its controlling grid, the d-c voltage being a resultant of the phase error between the incoming sync signal and a sawtooth voltage derived from the output of the horizontal sweep amplifier. This voltage is called an automatic frequency control (AFC) voltage. John F. Rider RadioFans.CN TV PAGE 1-54 GE MODEL 802GENERAL ELECTRIC CO. Fig. 6. Hor. Multivibrator and Sync The AFC voltage is developed by the diode-connected triodes V17A and V18A by mixing the horizontal sync pulses at the secondary of transformer T19 with a sawtooth voltage waveform derived at the output of the sweep amplifier tube, V22, when the sync pulse occurs at the time a shown in the sawtooth wave- form drawing in Figure 6, no voltage will be developed at the output of the filter. However, if the multivibrator runs faster or slower so that the pulse falls at a point other than at a, a positive or negative voltage will appear at the filter, which will be amplified by the d-c amplifier VI7B and then applied to the grid of the multivibrator. This change in d-c voltage on the grid of the multivibrator will cause it to speed up or slow down so as to cause the sawtooth wave to combine with the incoming sync pulses until the correction voltage becomes zero. With the filter consisting of R40, C59, and C49, the change is relatively slow in controlling the speed, permitting the equivalent of individual frame synchronization instead of each component line. This gives a picture characterized by greater detail than is possible where random noise triggers the directly synchronized sweep generator. The Horizontal Hold control, R86, in conjunction with the cathode tuned circuit C99 and L33, control the free-running speed of the multivibrator. They are adjusted near to the correct frequency during the time when no sync pulses are available. 6. HORIZONTAL SWEEP OUTPUT (SEE FIGURE 7)The hori- zontal sawtooth voltage generated by the multivibrator, V21, is shaped and then amplified by a Type 6BG6G tube, V22. The output of this tube is coupled to the horizontal deflection coils through an impedance-matching transformer, T25. An oscillatory voltage, as shown in the dotted line in the waveshape at the. upper left of Figure 7, which results from the rapid retrace in the trans- former T25, is removed by the damping tube, V23. This tube is a dual triode, Type 6AS7G, and by its use the transient may be dampened, linearity controlled, and the positive overshoot voltage retained for use in the high voltage supply. The linearity of the horizontal trace is controlled by varying the voltage wave- shape applied to the grid of V23 by potentiometer, R115. The horizontal size is controlled by the adjustable iron core induct- ance, L23, which is in series with the output to the yoke. Fig. 7. Horizontal Sweep Output 7. VERTICAL MULTIVIBRATOR AND SWEEP OUTPUT (SEE FIG- URE 8)The vertical sawtooth voltage is generated by a Type 6SN7GT tube, V19, connected as a multivibrator. This voltage is coupled directly to a Type 6V6G vertical sweep output tube, V20, and then to the vertical sweep coils through the impedance- Flg. 8. Vertical M.V. and Sweep Output matching transformer, T20. Vertical speed is controlled by changing the time constant of the multivibrator grid circuit by the potentiometer, R46. Sweep size is changed by the potenti- ometer, R49, which changes B+ voltage applied to the charging network of tube VI9 simultaneously with the screen voltage on tube, V20. Vertical linearity is controlled by a correction voltage developed in the cathode of V20 being fed back through C92 to the grid of the output tube. The amount of correction voltage is varied by the variable cathode resistor, R58. 8. HIGH VOLTAGf SUPPLY (SEE FIGURE 7)The high voltage is derived by making use of the inductive kick voltage produced during retrace in the horizontal- mtput transformer. This kick voltage is shown in the waveshape shown as c to b in Figure 7. This voltage is generated in the primary winding and is further increased by an additional winding added to the transformer which connects to the rectifier tube plate of V25. The rectifier tube, V25, is a Type 8016 which derives its filament voltage from the horizontal sweep transformer T25 by a single turn around the transformer. Because of the high frequency (15,750 cps) which is rectified, a 500 mmf. capacitor is more than sufficient for filtering purposes. 9. 1OW VOLTAGE POWER SUPPLY Two rectifiers are used to supply the required plate current for the television and radio receiver. A Type 5U4G tube, VI1, supplies the bulk of the current and makes use of a choke, L21, and capacitor, C106 and