Westinghouse-Electric-Corp-H-698P7 电路原理图.pdf

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1、AUDIO OUTPUT VOLUME R-20, MOST-OFTEN-NEEDED i960 RADIO SERVICING INFORMATION WESTINGHOUSE Models H-697P7, H-698P7, H-699P7, Chassis V-2393-3 a Also used in Montgomery Ward Model GTM-1201A i (Continued on page 149, at right) CHASSIS REMOVAL 1. Remove the tuning knob as follows. Insert a loop of strin

2、g (see figure 1) under the tuning knob and pull the knob up and out of the cabinet front. 2. Remove the back of the cabinet by loosening the two coin-slot screws on the back. 3. Remove the two 1 long hex head screws securing the chassis to the cabinet front. 4. Remove the printed circuit chassis, ba

3、ttery case, speaker spacers, rubber grommet and speaker. 5. To insert the printed circuit chassis back into the cabinet use the reverse procedure. The tuning knob and cabinet back screws must be the same or identical to the original dimensions to prevent possible damage to the tuning gang. hi g 5* f

4、i e 5! is H s| i s S* W ggf * E TUNING KNOB REMOVAL INSERT STRING UNOER TUNING KNOB 5 PULL UP Figure 1 Toning knob remove/ NEW CIRCUIT FEATURES This receiver incorporates new circuitry not previously used in Westinghouse radios. This is the use of a trans formerless audio output circuit and an impro

5、ved transistor detector circuit having amplified AGC and DC coupling to the Audio Driver stage. These new circuits provide improved fidelity, less distortion and more uniform operation. In the transformerless audio output circuit the trnasistors are operated in “push-pull” with each conducting for a

6、p proximately 50% of each cycle. Both transistors are biased close to cutoff, so that with no AC signal, both are effec tively not conducting. Out of phase audio signals are fed to the base of each transistor from the secondaries of the audio driver transformer (T4). Each transistor now conducts on

7、alternate half cycles of the incoming signal. The collector- to-emitter AC currents of each transistor alternately flow through the speaker voice coil. The need for a blocking capacitor between the detector and audio driver circuits is eliminated by locating the detector audio load (volume control)

8、in the detector emitter circuit. The AGC voltage is taken from the collector load of the transistor and therefore provides a greater range of AGC control voltage. The detector transistor is biased at near cutoff. The base-to-emitter circuit of the transistor thus acts as a diode, rectifying the IF s

9、ignal (detection). The ampli fied DC voltage, proportional to the IF signal level appears across R13and is used for AGC. The AGC voltage is filtered by Cll and coupled to the base of the 1st IF amplifier through RIO. _ 148 收音机爱 好者资料库 RadioFans.CN VOLUME R-20, MOST-OFTEN-NEEDED 1960 RADIO SERVICING I

10、NFORMATION WESTINGHOUSE Chassis V-2393-3, Loosely couple *teP modulated signal to: Loop LI setting Adjust for maximum: 455KC maximum T3, T2 and T1 in order indicated for max. output: (Reduce generator output if necessary for T2 and Tl adjustments.) 1625KC minimum Oscillator trimmer “D* 1400KC 1400KC

11、 RF trimmer “B” 600KC 600KC Oscillator coil, L2, if necessary Repeat steps 2, 3 & 4 C2 - 3 # 5 V T* I “vw-AJ / E ( B) ist |.F. AWPt css _ I _ 1 4 i 13 I TO ( s T2 n 3. TO SPEAKER - VOICE COIL (4) PENLIGHT CELLS (6 VOLTS) rtlllFTl|lFi ANT OSC. TRIM TRIM / r-vVf - CONVERTER 9 5.6V B+ /B IE Cj E C I I 1 / 7 L2 C3 CD j / + j Ur,s WJT ,v V? Im i * T i rat / styprsv Bottom view of printed circuit chassis with components shown as electrical symbols AUDIO OUTPUT (MATCHED PAIR) 149 收音机爱 好者资料库 RadioFans.CN