Zenith-Radio-Corp-S-14031 电路原理图.pdf

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1、MANUAL OF I9SI MOST-OFTEN-NEEDED RADIO DIAGRAMS ZENITH RADIO CORP. COBRA-MATIC RECORD CHANGERS MODELS SI4028. SI4029. SI4030. S14031 and S14036 The Zenith Models S-14028, S-14029, S-14030, S-14031 and S-14036 Record Changers are designed to play standard 78, 45 and 33 1/3 RPM records of standard com

2、mercial dimensions. With few minor exceptions these five changers are alike electrically. Features of these changers include playing and auto matically changing as many as ten 12” or ten 10” records. Ten inch and twelve inch records of the same type cannot be intermixed. A full stack of 7” 33 1/3 RP

3、M, or a full stack of 7” 45 RPM records (with adapter inserted in the records) can also be played on this changer. This changer does not shut off after the last record, however, all that is required to turn the changer off is to move the speed change lever (18) to OFF position. LOADING THE RECORD CH

4、ANGER 1. Pull straight up on the record pressure arm knob (12) until the record pressure arm clears the spindle. Swing the record pressure arm to the right until pins in pressure arm shaft (14) drop into locating slot on record pressure arm housing (1). 2. Changer will automatically play ten 12” eit

5、her standard or Long Play, ten 10” either standard or Long Play or ten 7” Long Play or Fine Groove records. NOTE: Standard, Fine Groove and Long Play records cannot be played in the same stack of records. Speed change lever (18) must be re-set for each type of recording. (Continued on page 160). REJ

6、ECT BUTTON RECORD CHANGER MOUNTING BOLT RECORD PRESSURE BAR TURN! RECORD CHANGER MOUNTING BOLTS TONE ARM 收音机爱 好者资料库 RadioFans.CN MANUAL OF 1951 MOST-OFTEN-NEEDED RADIO DIAGRAMS ZENITH Record Changer, continued To play 33 1/3 rpm records: 3. Place records on spindle and lower them to offset Motor spe

7、ed change lever ( 1) must be in 33 1/3 shelf. T.evel records and reDlace record Dressure position. 3. Place records on spindle and lower them to offset shelf. Level records and replace record pressure arm (14) over spindle and lower this until it rests on the top of the record stack. To play standar

8、d 78 RPM recordings: 1. Motor speed control lever (18) must be set to 78 position. This will set the record changer to proper speed position and cause the turntable to rotate. 2. Set-up lever (17) must be moved to the size records being played. 3. Place the changer in cycle by depressing reject swit

9、ch knob (73). The changer will play the remain ing records automatically. The changer will continue to play the last record until speed change lever (18) is moved to OFF position.i 12,- 2. Set-up lever (17) should then be moved to either 12”, 10” or 7” position depending on the size record being pla

10、yed. To play Fine Groove (45 RPM) records: 1. Speed change lever (18) should be moved to 45 position and set-up lever (17) should be in 7” position. It must be remembered that these records are manu factured with a I 1/2” spindle hole so it is essential that a record adapter be inserted into each 45

11、 RPM record to be played. This is necessary to reduce the spindle hole to conventional size. V & I 160 8 9 74 10 I! Record Changer Top View with Turntable Removed 收音机爱 好者资料库 RadioFans.CN MANUAL OF 1951 MOST-OFTEN-NEEDED RADIO DIAGRAMS REJECTING ZENITH Record Changer, continued To reject a record any

12、time, while the changer is op- STOPPING erating, depress reject switch button (73) and release. . This will automatically cause the record changer to go To turn off the record changer all that is required is through cycle and begin playing the next record. to move the speed shift lever (18) to OFF p

13、osition. 43 66 58 65 59 62 收音机爱 好者资料库 RadioFans.CN MANUAL OF 1951 MOST-OFTEN-NEEDED RADIO DIAGRAMS ZENITH Record Changer, continued UNLOADING Lift the record pressure arm (14) and swing it to the right until the pin on the shaft drops into the locating groove on record pressure arm shaft housing (1)

14、. Lift stack of records straight up on spindle. MANUAL OPERATION To play single records or home recordings, lift up the record pressure arm and turn it to the right. Place record on spindle and lower to the spindle shelf. Gently push record towards record pressure arm shaft and lower to turntable. M

15、ove speed change lever (18) to proper speed for type of record being played and move set-up lever (17) to manual position. Pick up tone arm and place the needle on the lead-in groove of the record. DESCRIPTION OF CYCLING The motor shaft contacts drive wheel assembly (36) and causes it to rotate by f

16、riction contact with its rubber surface. Drive wheel assembly (36) drives idler wheel (5). The underside of the turntable is in contact with idler wheel (5) and is driven in this manner. Speed of the turntable is controlled by changing the position of the idler wheel (5) on drive wheel (36). When id

17、ler wheel is moved to the center of drive wheel (36) it will rotate more slowly than when moved to the outer edge of this drive wheel (36). In this manner the turntable can be driven at any speed from 10 to 85 RPM. Minor adjustments for proper tonal pitch can be made by simply moving speed change le

18、ver (18) back and forth to compensate for turntable speed which may vary due to line voltage changes. When reject button (73) is depressed it energizes solenoid (61) which then attracts trip pawl assembly (62). The same thing occurs when the for ward movement of the tone arm causes friction lever an

19、d weight assembly (47) to contact the copper bronze contact on trip switch assembly (63). When gear seg ment (58) is released, gear pawl spring (42) causes the gear segment (58) to engage the rotating pinion gear (25) under the turntable thus causing clutch assembly (41) to rotate. As clutch assembl

20、y (41) rotates, tone arm lift lever (46) swings in such a manner that it contacts tone arm lift pin and raises the tone arm. Simultaneously, tone arm link and stud assembly (56) slides towards, and contacts one finger of tone arm lever assembly (49) forcing the tone arm towards the outer edge of the

21、 turntable and then on its return swing contacts the other finger of tone arm lever assembly (49) swinging the tone arm back over the records. The position to which it swings the tone arm over the records is de termined by the position of record size discriminator (51). There are three steps on the

22、record size dis criminator (51) which determines set-down position 168 for 7”, 10” and 12” records. The tone arm lift lever (46) returns and releases brake lever assembly (48) which keeps the tone arm from moving erratically during cycle. Simultaneously, ejector lever and link assembly (59) rotates

23、and this in turn causes spindle shaft (30) to rotate and ejector cam (29) to push the record off the spindle shelf. Operation of the tone arm set-down adjustment can be observed by raising the tone arm so the adjustment mechanism can be viewed, VELOCITY TRIP This changer is provided with what is com

24、monly known as a velocity trip rather than a ratchet and positive trip mechanism. A velocity trip depends for the tripping action on the rate of forward motion of the pickup arm with respect to the turntable ro tation. The changer will trip only when the tone arm advances more in one revolution of t

25、he turntable than the distance between normal grooves in a record. Only records having fast finishing grooves will operate the velocity trip. During the normal playing cycle, friction lever and weight assembly (47) continually moves forward toward the copper bronze contact on trip switch assembly (6

26、3). On normal forward advance, the friction lever and weight assembly (47) is kept from contacting the copper bronze contact by a wiping action from oscil lating lever stud assembly (55). The oscillation of os cillating lever and stud assembly is produced by eccentric motion of oscillating gear (4)

27、which is driven by the pinion gear (25) on the lower portion of the turn table. Oscillating gear (4) is mounted off-center so it will descrioe an eccentric action as it is being driven by the turntable gear. The tone arm moves in towards the center of the record and the repeated action of oscillatin

28、g lever (55) keeps friction lever and weight assembly (47) from coming in contact with the copper bronze strip on trip switch assembly (63) as the pickup arm moves slowly towards the spindle and lead-in grooves. During the first revolution of the turntable, in the eccentric cycling grooves, the pick

29、up arm ad vances rapidly and friction lever and weight assembly (47) is moved forward fast enough so that oscillating lever (55) does not halt its progress, therefore, friction lever and weight assembly (47) contacts the copper bronze trip contact on trip switch assembly (63) grounding it and making

30、 a complete circuit. This actuates solenoid (61) causing the changer to cycle. THEORY OF THE COBRA RADIONIC PICKUP The operation of the Cobra pickup is considerably different from Crystal and Dynamic pickups. These pickups generate audio power, while the Cobra con trols power generated by a radio fr

31、equency oscillator, detector and audio amplifier. The oscillator operates at a frequency of 2.5 Me. Modulation is accomplished by changing the energy losses in a tuned circuit. These losses may be represented by an equivalent resistance in series with the reactance of the coil. The ratio of the resi

32、stance to the reactance determines the effi- MANUAL OF I9SI MOST-OFTEN-NEEDED RADIO DIAGRAMS ciency or Q of the coil. The amplitude of the RF voltage developed across this coil by an oscillator will vary with changes in Q. The grid coil LI and other components of the oscil lator are mounted in the o

33、scillator pre-amp chassis, while the plate coil L2 is in the needle cartridge with vane and needle assembly. The coil is fixed and has 40 turns of No: 40 wire (approximate DC resistance 2 1/2 ohms). The stainless steel vane, which is in the field of the coil, is spot welded to the osmium-iridium tip

34、ped stylus. Any movement of the stylus will cause a corresponding movement of the vane. As the stylus and vane follow the modulations in the record, changes in the mutual inductance between the vane and coil occur. In posi tion 2 the vane is at rest, and a constant RF voltage appears across the plat

35、e coil. As the vane is set in motion and reaches position 1, it is at its greatest outward swing from the coil, resulting in low mutual inductance, low reflected resistance, higher Q, and a higher RF voltage across the coil. In position 3 it is at its greatest inward swing, resulting in a high mutua

36、l inductance, high reflected resistance, lower Q and a e * ZENITH Record Changer, continued lower RF voltage. It can be seen that the amplitude of the RF voltage which appears across the coil will vary with changes in Q, satisfying the condition for ampli tude modulation. The position of the vane ch

37、anges both the Q and L of the coil. Changes in L shift the fre quency slightly, and a certain amount of frequency modulation is present, but since there is no frequency discrimination it remains undetected. Since the grid and plate coils are part of a single tuned circuit, any variations of amplitud

38、e of the RF voltage brought about by the changes in Q across the plate coil will also appear across the grid of coil LI, causing a shift in the average plate current through the plate load resis tor across which the audio output voltage is developed. Plate bend detection takes place since only the p

39、ositive half of the grid swing causes an increase in the av erage plate current. These changes in the average plate current appear as audio voltage across the plate load resistor. The 2.5 Me RF voltage and the audio voltage both appear at the plate-(pin 6) of the oscillator triode. R2, C4 and C5 fil

40、ter out the RF voltage allowing only the audio component to the grid (pin 4) of the amplifier triode where it is amplified, fed through a shielded lead to the audio amplifier of the receiver and repro duced by the loud speaker. SET DOWN ADJUSTMENT When adjusting the tone arm for proper set-down on t

41、he edge of the record, move set-up change lever to 7” position, place a 7” record on the turntable, turn the record changer through cycle by rotating the turntable by hand. Watch closely where the needle point of the Cobra cartridge lands on the record and adjust tone arm set-down adjustment screw (

42、33) until proper landing position is obtained. I MANUAL OF I9SI MOST-OFTEN-NEEDED RADIO DIAGRAMS I ZENITH Record Changer, continued Tone Arm Set-Down & Height Adjustments TONE ARM HEIGHT ADJUSTMENT The tone arm height adjustment determines vertical rise of the tone arm. If the tone arm does not rise

43、 sufficiently it will not play a full stack of twelve re cords. On the other hand, if the tone arm raises too high it may hit the records resting on the record shelf. Set the tone arm height adjustment screw (32) so that the needle clears twelve unwarped records on the turntable. The tone arm housin

44、g must not hit the under side of the records on the record shelf when the changer is cycled after adjustment. SLAB HEAD SCREWS For maximum rigidity many components are locked into position with slab head screws. This type set screw provides a more positive grip. The slab head set screw wrench is ava

45、ilable as part number 68-8. pulled off spindle assembly (72) and if this does occur, it can easily be replaced by sliding a new spindle cap down over the spindle and then pressing in on the de tent portion, which acts as a stop to keep the spindle cap from sliding off spindle (72). If breakage occur

46、s other than loss of the spindle cap (31), the entire spindle assembly (72) must be replaced. SPEED INDICATOR ADJUSTMENT SPINDLE The spindle on this record changer is composed of five separate parts: Spindle shaft (30) and ejector cam (29) are pressure-fit together and if either breaks, they cannot

47、be replaced since the assembly operation is a machine operation. The spindle housing is composed of two separate portions which once again are pres sure-fit together and require a machine operation for assembly. It is possible that spindle cap (31) may be 164 It is possible that the speed of the rec

48、ord changer may not conform to the speed stop on escutcheon (23). Proper adjustments can be made in the following 36 manner. Put a stroboscopic disc on the turntable, adjust speed change lever (18) until the turntable is turning at exactly 78 RPM. Stop the record changer by pulling the AC plug, remo

49、ve the turntable, loosen the two adjusting screws (74) and move speed change lever (18) so that the point on the control knob indexes exactly at the 78 mark on the escutcheon (23). Then re-tighten adjusting screws (74) and replace the turn table. The turntable should now rotate at exactly 78 RPM, however, as a precaution, again check with the stroboscopic disc.