Zenith-Radio-Corp-7XT40-2 电路原理图.pdf

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1、VOLUME R-17, MOST-OFTEN-NEEDED 1957 RADIO SERVICING INFORMATION CHASSIS 7XT40 CHASSIS 7XT40 CHASSIS 7XT40Z CHASSIS 7XT40Z1 CIRCUIT #1 CIRCUIT #2 MODEL “ROYAL 500” ALL TRANSISTOR RADIO Material on Chassis 7XT40, Circuit #1, (Black code dot), is printed on page 184, in Volume 16, 1956 RADIO Diagram Ma

2、nual. Service material on these receivers using the other circuits is printed below and on pages 187 through 189. The “Royal 500“ seven transistor portable has been produced with four basic chassis. This expedient was necessary to enable us to produce sufficient quantities by using transistors from

3、many sources. All chassis have the chassis number stamped on them as well as a color identifying code on the battery compartment just above the battery installation instruction label. They are as follows: Chassis 7XT40 - (Black) code dot Chassis 7XT40 - (Maroon) code dot Chassis 7XT40Z - (Red) code

4、dot Chassis 7XT40Z1 (Green) code dot The two 7XT40 chassis are very similar wilih the exception of the different coding on transistors. The transistors in these two chassis are manufactured by Sylvania. The 7XT40Z uses transistors manufactured by Raytheon Mfg. Co. The 7XT40Z1 uses transistors manufa

5、ctured by Texas Instruments Inc. In addition to this, each receiver has its individual transistor lay out label and the color of the printing on these labels as well as the chassis number on these labels conforms respectively to the color dot and chassis number. You will note that the initial 7XT40

6、circuit diagram illustrates an external earphone connection at the output of the driver trans istor. This is also true of all the other chassis manufactured up to serial no. 33240. These chassis use an earphone part no. 39-20 which has an impedance of 2,000 ohms. Later on in receivers manufactured a

7、fter serial number 33240, the earphone jack will be removed from the driver circuit and placed in the speaker voice coil circuit. A new earphone with an impedance of 15 ohms, part no. 39-22, will be required for this circuit. ENGINEERING MODIFICATIONS Since transistor circuitry is new and improvemen

8、ts are continu ally being discovered. Circuit 1 is for the original 7XT40 Chassis. The engineering staff has found ways to improve the AGC system as well as other portions of the circuitry. Therefore, the follow ing engineering changes are design improvements on the original 7XT40 (See Circuit 2,7XT

9、40). Originally the bias bleeder oh the first IF stage was 100K and 15 K plus a 2 K volume control from B + to ground. The AGC by-pass of 3 mfd was at the junction of the 100 K and 15 K which meant that there was 15 K in series with the AGC current. During production the amount of AGC was found to b

10、e insufficient. The bias bleeder was then changed to 100 K, 4700, 4700 and 5 K volume control. The AGC by-pass of 16 mfd was put between the two 4700 ohm resistors. 4700 and 47 K in junction with 05 and 06 were 2200 and 18 K respectively. This change was made to stabilize collector current of the dr

11、iver transistor and slightly increase its gain. In the event you do not wish to modify the circuit as in item 1, it is suggested that when servicing sets which exhibit AGC and overload problems, the bias bleeder of the first IF stage be changed. The original circuit had a 100 K and 15 K. These value

12、s should be changed to 47 K and 4700 ohms respectively. This in effect supplies more AGC voltage to the mixer and first IF. You will note that C5 and C6 in the revised 7XT40 diagram have been terminated at ground and of course then the 470 ohm resistor from the 1st IF emitter must be by-passed with

13、C23 a .05 condenser. C7 and C8 are terminated at ground for production convenience. The 7XT40Z has not had any modifications up to the present time. The 7XT40Z1 - 1. The 2200 ohm bias resistor in the 121-17 second IF transistor was 4700 ohms. It has been changed to 2200 ohms to reduce tweet, by slig

14、htly lowering gain. 2. I K resiitor in the emitter of the 121-16 mixei was 470 ohms. This change was made to reduce tweet and noise. 3. On the patent & transistor layout label for 7XT40Z1 (Green Printing) the mixer transistor was marked 121-6. This was a typographical error and it should be 121-16.

15、ALIGNMENT PROCEDURE |h,|a, onnect saart1 & T T emitterI BASE- COLLECTOR- 455 KC Chassis ONE 600 KC Adf.-n.n. T3 for maxi* mum output* For I.F. Alignment 1620 KC TURN _ LOOSELY Gang wide open CIC Set oscillator to dial scale 1260 KC COUPLED TO 1260 KC CIA Align leap antenna 535 KC WAVEMAGNET Gang dos

16、ed Adjust slug in T6 Set esdlletor te dial scale REPEAT STEPS 2, 3 AND 4 186 收音机爱 好者资料库 RadioFans.CN VOLUME R-17, MOST-OFTEN-NEEDED 1957 RADIO SERVICING INFORMATION ZENITH RADIO Model Royal 500 Transistor Radio, Continued For schematic diagram of 7XT40, Circuit #1, (Black code dot), see page 184 of

17、Supreme Publications Volume 16, Most-Often-Needed 1956 Radio Diagrams. SCHEMATIC DIAGRAM FOR 7XT40 CIRCUIT #2 CIC OSC. TRIM. CIC OSC TRIM. TRANSISTOR b TRIMMER LAYOUT TRANSISTOR b TRIMMER LAYOUT FOR 7XT40 CIRCUIT #2 FOR 7XT40Z 187 收音机爱 好者资料库 RadioFans.CN ZENITH RADIO Model Royal 500 All Transistor R

18、adio, Continued 121-14 121-10 121-10 121-11 MIXER 1ST I.E 2ND I.E DRIVER 1 T 1-1 1 -trir IK CIS _T* /I , 81 T4 CRN 121-12 OUTPUT denotes CHASSIS EMITTER SASE- COLUCTOR-1 8E- EMITTIN COLLECIOR TRANSISTORS SCHEMATIC DIAGRAM FOR 7XT40Z 收音机爱 好者资料库 RadioFans.CN VOLUME R-17, MOST-OFTEN-NEEDED 1957 RADIO SERVICING INFORMATION ZENITH RADIO Additional Variations on Model Royal 50011 Radio, Continued SCHEMATIC DIAGRAM FOR 7ZT40 2N35 SCHEMATIC DIAGRAM FOR 7ZT40Z1 I2H6 121-17 121-17 I2H8 121-19 MIXER 1ST If 2NDI.E DRIVER OUTPUT 189