120 Cohassett St Pittsburgh11 Pa Here's Why Vibrators Are Quiet, Reliable and Longer Lasting!

aaíTtliitaaaass re3« aft=I=an aa 4'14 agaaaa :aAnts Vol. 14 AUGUST, 1949 No.8 CORNELL-DUBILIER ELECTRIC CORP. Hamilton Boulevard, South Plainfield, N. J. Sec.562, P.L.&R. U. S. POSTAGE POSTMASTER:Ifundeliverable for any reason, notify stating reason, on Form 3547 postage for PAID which is guaranteed. So. Plainfield, N. J. Permit No. 1 MR BLRTR ÁM B HOFFMANI-11 120 COHASSETT ST PITTSBURGH11 PA HERE'S WHY VIBRATORS ARE QUIET, RELIABLE AND LONGER LASTING! C -D designed electronic micrometric equipment re- moves guesswork in contact point setting and assures consistent high quality. Exclusive C -D polepiecedesign and armature weight resultsinaperfectly -balanced unit with greater efficiency. Exclusive C -D base mounting results in "a full floating unit.That's why C -D vibrators last longer. Unit completely enclosed in new floating sock- an exclusive with C -D vibrators.Eliminates usual difficulties found in other vibrators. New stack design will take peak voltages of even 4,200 volts with no damage to vibrator. For the best in Vibrators insist on C -D's. Now at your local C -D distributor. 1949 Or write for full details to Cornell- Dubilier Electric Corp., Dept. H09, South Plainfield, N. J. Other plants in New Bedford, Worcester, and Brookline, Mass.; Providence, R. I.; Indianapolis, Ind.; and Cleveland, Ohio. A GREAT NAME IN CAPACITORS A GREAT NAME IN VIBRATORS. For your nearest C -D Distributor, consult your local Classified Telephone Directory THE HOW AND WHY OF VIBRATORS History and Development PART II Intheprecedingissuethebasic switch and magnetic coil, energizing theory upon whichthesatisfactory the latter and pulling the switch arm operation of a vibrator depends was toward it. This opens the transformer developedandillustrated.Itwas circuit and releases the magnetic pull shown that in order to have a satis- of the switch coil, allowing the switch factorysubstitute forasetof "B" toclose, again starting the cycle of batteries,acorrectly designed com-events just described. So long as the bination of certain components was battery has energy available the switch required. This combination consisted will continue to operate at a regular of a low -voltage DC source, such as rate, this depending upon the rate of a storage battery, an inverter, a transformer, arectifier, and afilter.The inverter was the only unusual com- VI BRATOR ponent in this group, and was required becausethetransformercouldnot II 1 50 function on the DC from the battery. Thus, a device must be inserted be- o tween the battery and the transformer to change the character of the DC so 6 V. thatitwould appeartothetrans- former to be AC. The vibrator is to III be the inverter in the combination of VIBRATOR POINTS OPEN components listed abode. 15 Lc) i VIBRATOR WAVE Our previousdiscussionalsode- J 10 (Er) veloped the necessary interdependence o of the vibrator, transformer, and the "buffer" capacitor, (where the vibrator had progressed as far as the pulsating VIBRATOR key in Figure 7), in the correct elec- POINTS CLOSE WAVE IF VIBRATOR trical operation of the power unit. We POINTS WERE KEPT were at the point where we were ready CLOSED LONGER to convert the manual key into an auto- matically -actuated vibrating switch, or Fig. 8. vibrator, and discuss its performance in the circuit. build-up of current in the circuit and Now refer to Figure 8. The circuit upon the mechanical characteristics of shown here is somewhat different from the switch. Thus the VIBRATOR be- that in Figure 7. The key of Figure 7came a reality, although the similarity has been replaced by a switch con- to the bell -buzzer of Figure 3 is readily trolled by the magnetic coil in series noted. with the battery and transformer pri- Another change shown in the circuit mary.When thebatterycircuitis of Figure 8isthe moving ofthe closed,themagnetizing currentfor Capacitor "C" from its former location thetransformerflowsthroughthe across the primary terminals to a new AUGUST, 1949 Page 3 location across the secondary terminals direct current to a load connected to of the transformer.Because the pri- theterminalsmarked"B+"and mary and secondary coils are usually "B-". If the rectifier tube is properly closelycoupled,theeffectofthe polarized for the primary battery con- capacitance across the secondary willnections, it will conduct current dur- be almost perfectly reflected into theing the portion of the cycle when the primary.However, since the tuningvibratorcontactsareclosed,(the effect of the secondary coil as com- square -toppedpulse),and afairly pared to the primary coil is dependent good efficiency will be realized.If upon the square ofthe number ofthe battery polarity is reversed, how- turns for eachcoil,(square of the ever,thepolarityofthesecondary turn ratio), the value of capacitancevoltage will be reversed and the recti- needed for proper equivalent tuningfier tube will now conduct only dur- usually is much smaller for connection ing the portion of the cycle when the in the secondary than for in the pri- vibratorcontactsareo p e n,(the mary circuit. For instance, if the turn -rounded pulse), and the only energy ratio is 50, the square of this numberavailable will be that storedinthe is2500,andthesizeofcapacitor core of the transformer andinthe neededforthesecondarywillbe buffer condenser. This results in low 1/2500 of that needed in the primary. output capabilities and poor efficien- The waveform resulting from the cies. circuit shown in Figure 8 is illustrated Several manufacturers produced "B" in the accompanying graph. The vi-eliminators ofthistype, which met brator characteristics of frequency and with rather wide acceptance and gave time efficiency can be so matched toreasonably good life and performance. the transformer characteristics and the One radio manufacturer produced a capacitance of "C" that the contacts open before the transformer core be- receiver in which he built in the power gins to saturate and close with theunit and thus made the forerunner tuned -circuit oscillation voltage prac- of the present type of set. There were tically equal tothe battery voltage. several inherent drawbacks to such a This circuit characteristic protects thedesign of power -unit, however, and it vibrator contacts from excessive spark- is desirable to outline these in order ing and electrical wear. If we connect to see the reasons for future develop- a rectifier tube and filter to the second- ments.The first,and possibly most ary of the transformer, as shown inobvious, difficulty lay in the method the circuit of Figure 9, we can supply ofdrivingthevibrator.Sincethe Es VOLTAGE ACROSS SEC. WINDING VOLTS VIBRATOR Ir111.ef CURRENT IN SEC. WINDING r i I i I I I I I I m t.. J 1= T y' T To PR I. 8 - Fig. 9. Page 4 THE C -D CAPACITOR driving -coilwasinserieswiththe After considerable thought, a simple primary circuit, all of the magnetizing change in the design of the vibrator and load current passed through theenabled the engineers to correct the coil and thus produced the magneticdifficulty encountered in driving the pullaffecting the movement ofthe vibrator.If we did not want the unit reed.Therefore,ifthe load currentto be sensitivetoload current, we changed, the magnetic pull changed should make its driving power depend- anddirectlyaffectedtheoperating ent upon the battery voltage instead, characteristics of the vibrator. Underwhich remains substantially constant. a no-load condition, the pull would beBy supplying a high -resistance voltage slightandthereedwouldmerely coil instead of the low -resistance cur- flutter.Under an overload condition, rent coil, and connecting this across the pull would be great and the reed thevibratorcontactsinsteadofin amplitude would be excessive. Underseries with them, we can make the both conditions the tuning of the cir-unit drive independently of the load cuit would be bad and severe sparking current.InFigure10 we seethis would result.With excessive ampli- arrangement, where the coilis ener- tude, reed breakage would probably occur.Thus, for a given design of power -unit, only a narrow range of loads could be handled.This was I I I partially met by the introduction of a o series of units with different values of outputloads,each having avi- brator with a coil designed for that load.These varied from a low of 1 about 135 volts at15 ma to a high I1 of 180 volts at 40 ma. The no-load SERIES COIL condition was sometimes taken care of by the use of a "phantom load", which was a resistor connected across the output until the set load became o large enough to operate a relay having a coil in series with the output circuit. o The fact that the system operated "half -wave" was anothersourceof 1 difficulty.The transformer core was SHUNT COIL subjected to pulses of DC load current, with the result thatinefficient Fig. 10. transformer action occurred, the core having a large residual magnetization in one direction.Thisfactlimited gized when the contacts are open, and the amount of energy that could be is shorted out when the contacts close. transferredtotheloadcircuit.In One other major differenceis now addition, it necessitated the use of an involved.At rest,the vibrator con- exceptionally large transformer in or- tacts must be open in order to start der to operate at low flux -densities. the vibrator with the shunt coil, while The other problem has already beenthey must be closed in order to start discussedina preceding paragraph, the vibrator with the series coil. where the relation between the polar- the To correct the inherent difficulties ityofthebattery andthatof

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