Thus voltage e has the same slope as the applied voltage times an exponential term which is determined by the resistance Rx of the amplifier, the OCL of the transformer, and the time between the beginning and the end of the linear sweep. Under the conditions assumed, the value of the exponential for any interval of time can be taken from the curve marked R2 = x> m Fig. 234. For example, suppose that the sweep lasts for 500 microseconds, that the sweep amphfier tube plate resistance is 800 ohms, and that the transformer inductance is 10 henrys. The abscissa of Fig. 234 is 0.04, and. since the slope of this exponential curve equals its ordinate, the slope of the voltage applied to the plates of the oscilloscope will be, at tiie end of the sawtooth interval, 96 per cent of the slope which it hud at the beginning of the interval.

Assume that at the end of the time interval t (Fig. 258) the amplifier tube is cut off. Then the sweep circuit transformer reverts to that of Fig. 235, in which Св has the same meaning as before but Ri includes only the losses of the transformer, which were neglected in the analysis for linearity of sweep. That is to say, the voltage does not immediately disappear but follows the curves of Fig. 235 very closely, as in magnetic deflection. Backswung voltage may be kept from affecting the screen by suitable spacing of the applied wave forms or biasing the cathode-ray tube grid.

Vertical sweep transformers are used in television receivers to displace the horizontal sweep lines at a 60-cycle rate, in order to produce a picture. The vertical displacement is fairly linear, retrace rapid, and sawtooth wave form is necessary here also. Because of the relatively slow vertical displacement, yoke inductance is negligible, so that vertical sweep amplifiers effecti\ely operate into resistive loads during trace periods. The transformers present no ])articularly difficult problem beyond that of high OCL at low cost.

141. Magnetic Sweep Circuits. A simple television receiver sweep circuit is shown in Fig. 260. Pulse voltage applied to tlie tetrode grid appears across the transformer primary winding inverted. Current in the lower part of the transformer primary has the shape shown in Fig. 257. This is the current wave shape in the transformer secondary and deflection coil (termed the yoke). An autotransformer extension of the transformer primary winding is used to transform the pulse voltage backswing shown in Fig. 257 to a high value. This voltage is actually much larger than Fig. 257 indicates, and needs only 3:1 step-up to furnish 7 to 14 kv. It is then rectified and applied to the accelerating anode of the oscilloscope. In this way, a separate

high-voltage supply is avoided. A damper diode is used to convert the backswing current into useful current during the next sweep in-

HV DIODE

-TO SCOPE 2ND ANODE

damper

Fig. 260. Television sweep circuit.

tetrode. conducting

damper diode conducting

yoke

voltage

terval. Backswing current reaches its negative peak at the end of retrace period т,-. As indicated by the dotted oscillation at the left of Fig. 261, this current would continue to oscillate for some time if left undamped. With the damper diode circuit, this current never oscillates but instead charges the diode R-c network, which slowly discharges into the yoke. Before damper current reaches zero, the tetrode starts to conduct. Because of winding capacitance, the tetrode tube current is not initially linear. It is offset by exponential decay of damper tube current. Yoke current then proceeds in a linear manner, following the dotted line in the transition from damper to tetrode current, as in Fig. 261.

With the large consumer demand for television receivers, there has been an incentive for improved efficiency of the basic sweep circuit. Partly this has been accomplished bv ingenious schemes for improved

Fig. 26L Deflection yoke current and voltage.

A-c SUPPLY

Fic. 262. Magnetk; pulse generator.

linear and re-onates with C\ at the supply frequency. Resonance therefore tends to maintain current г sinusoidal in wave form. Current i is large enough to saturate reactor L2, which has rectangular B-H loop core material. Twice each cycle current i passes through zero, and near these current zeros L2 inductance becomes large. This large inductance forces most of current i instantaneously into C2 and Rl, and builds up a comparatively large jeak voltage across Rj,. Such pulses are peaked in wave shape and alternate in polarity twice each cycle. Pulse durations of less than 0.1 microsecond have been obtained with this circuit. Owing to the large interval of time during which i is large, and not producing pulses, the power output is limited to small values.

In Fig. 262 the voltage across L2 at a given line frequency / is nearly proportional to the saturation flux density Bg of the core for rectangular loop material. If the core area is Af and turns Л in L2, then this Voltage is, neglecting losses,

1 See Television Deflection Circuits, by A. W. Friend, RCA Rev., March. 1947. p. 98; also Magnetic Deflection Circuits for Cathode-Ray Tube.s, by O. H. Schade, RCA Rev., September, 1947, p. 506.

linearity with lower transformer Q, and partly by using the plate input resistance of the tetrode for the damper diode bias resistance. Thus otherwise wasted power is put to a useful purpose.

142. Magnetic Pulse Generators. In Chapter 9 it was seen that thyratron operation can be approximated by self-saturating magnetic amplifiers. This fact points to a saturable reactor to replace the hydrogen thyratron in the pulser of Fig. 252. Several factors militate against the direct substitution of saturable reactor.s for thyratrons:

1. Departure of core material from sharp rectangularity interferes with steep pulse voltage rise.

2. Saturated value of inductance interferes with large current flow needed during pulse.

3. Reactors are a-c devices; hence a-c charging must be used. This limits the choice of PRF.

Despite these difficulties, saturable reactors have been used successfully in pulsers. Low power pulses may be formed by use of the circuit of Fig. 2(i2. Reactor Li is

(145)

where ва/2 is the angle, starting from zero, at which saturation is reached, as in Fig. 193 (p. 247). If 6 is very small, and 2ж/сс RlCz в^/ш, substantially all of appears across Rl-

Higher power may be obtained from cascaded stages as in Fig. 263.

TO A-c SUPPLY

Eio. 263. Cascaded stages in magnetic pulse generator.

Reactor Li is linear and resonates with Ci at the supply frequency. Reactors L-j, L-.i, and l4 are saturable; bias windings are used, but not shown. Suppose that L2 and are initially unsaturated, and is saturated. Ci charges in series with and L3. As the voltage across L2 reaches maximum, L2 saturates and discharges Ci. Discharge current causes l3 to become unsaturated and l4 saturated; then C2 charges until L;j saturates again. As the wa\e proceeds towards Rl both charge and discharge times become successively shorter. Pidse duration in each stage is determined by the saturated value of inductance and associated C. In the last stage, the pulse is shaped by PFN to the desired duration and flatness at the top. As this sequence is repeated once each cycle, the line current is not sinusoidal, so a line capacitor is useful for supplying the current harmonics. One modification of this circuit is the use of saturating transformers instead of reactors in order to provide the stepped-up voltage necessary for magnetron operation. With a magnetron, R is replaced by a pulse ransformer primary winding. In another modification saturable reactors are the series elements and capacitors the shunt.

1 See The LTse of Saturable Reactors as Dis<harge Devices for Pulse Generators, by W. S. Melville, J.I.E.E. (London), 08, Part Ш, p. 185.

BIBLIOGRAPHY

transformer theory

1. E. G. Reed, Essentials of Transformer Practice, McGraw-Hill Book Co., 2nd ed., New York, 1927.

2. L. F. Blume, Editor, Transformer Engineering, John Wiley & Sons, 2nd ed., New York, 1951.

3. M.I.T. Electrical Engineering Staff, Magnetic Circuits and Transformers, John Wiley & Sons, New York, 1943 (contains extensive bibliography).

core materials

4. Magnetic Core Materials Practice, Allegheny Steel Co., Brackenridge, Pa., 1937.

5. J. K. Hodnette and C. С Horstman, Hipersil, a New Magnetic Steel and Its Use in Transformers, Westinghouse Engineer, 1, 52 (August, 1941).

6. A. G. Ganz, Applications of Thin Permalloy Tape in Wide-Band Telephone and Pulse Transformers, Trans. AIEE, April, 1946, p. 177.

7. ASTM Standards on Magnetic Materials A34-49 to A345-49 inclusive, American Society for Testing Materials, Philadelphia, Pa.

8. R. M. Bozorth, Ferromagnetism, D. Van Nostrand Co., New York, 1951.

9. C. C. Horstman, Progress in Core Material for Small Transformers, Westinghouse Engineer, 12, 160 (September, 1952).

10. S. R. Hoh, Evaluation of High Performance Magnetic Core Materials, Tele-Tech, 12, 86 (October, 1953).

11. James R. Wait, Complex Magnetic Permeability of Spherical Particles, Proc. I.R.E., 41, 1664 (November, 1953).

rectifiers

12. D. C. Prince and P. B. Vogdes, Mercury Arc Rectifiers, McGraw-Hill Book Co., New York, 1927.

13. A. J. Maslin, Three-Phase Rectifier Circuits, Electronics, 9, 28 (December, 1936).

14. D. L. Waidehch and H. A. Taskin, Analyses of Voltage-Tripling and -Quadrupling Circuits, Proc. I.R.E., S3, 449 (July, 1945).

15. R. S. Mautner and O. H. Schade, Television High-Voltage R-F Supplies, RCA Rev., 8, 43 (March, 1947).

16. E. V. Blieux, High-Voltage Rectifier Circuits, General Electric Rev., 61, 22 (February, 1948).

REACTORS

17. T. Spooner, Effect of a Superposed Alternating FieM on Apparent Magnetic Permeability and Hysteresis Loss, Phys. Rev So (2nd series), 527 (January-June, 1925).

18. L. B. Arguimbau, P. K. McElroy, and R. F. Field, Iron-Cored Coils jor Use at Audio Frequencies, General Radio Co., Cambridge, Mass.

19. V. E. Legg, Optimum Air Gap for Various Magnelic Materials in Cores of Coils Subject to Superposed Direct Current, Trans. AIEE, 64, 709 (1945).

20. George Katz, Effect of Temperature on Iron Powder Cores, Elec. Mfg., 63, 135 (February, 1954).

AMPLIFIERS

21. H. S. Black, Stabilized Feedback Amplifiers, Bell System Tech. J., 13, 1 (January, 1934).

22. R. Riidenberg, Electric Oscillations and Surges in Subdivided Windings, ,/. Avpl. Phys., 11, 665 (October, 1940).

23. F. E. Terman, Radio Engineers Handbook, McGraw-Hill Book Co., New York, 1943, Sections 2 and 3.

24. K. Schlcsinger, Cathode Follower Circuits, Proc. I.R.K., 33, 843 (December, 1945).

25. H. W. Bode, Network Analysis and Feedback Amplifier Design, D. Van Nostrand Co., New York, 1945, Chapters XVI to XIX.

26. D. T. N. Williamson, Design for a High-Qua!ity Amplifier, Wirele,ss World, April, 1947, p. 118.

27. H. W. Lamson, Advantages of Toroidal Transformers in Communication Engineering, Tele-Tech, 9 (May, 1950).

28. T. Halabi, Audio Transformer Design Charts, Electronics, October, 1953, p. 193.

NON-SINUSOID.AL WAVES

29. J. G. Braincrd, G. Koehler, H. J. Reich, and L. F. Woodruff, VUra-High Frequency Techniques, D. Van Xostrand Co., Xew York, 1942, pp. 36-47.

30. H. E. Kallman, R. E. Spencer, and C. P. Singer, Transient Response, Proc. I.R.K., 33, 169 (March, 1945).

31. C. E. Torsch, A Universal-Application Cathode-Ray Sweep Transformer with Ceramic Iron Core, Proc. Natl. Electronics Conf.. 130 (1949).

32. L. W. Hussoy, Non-Linear Coil Generators of Short PuLses, Proc. I.R.E., 38, 40 (January, 1950).

33. H. W. Lord, A Turns Index for Pulse Transformer Design, Trans. AIEE, 71, Part 1, pp. 165-168 (19.52).

34. M. Chodorow, E. L. Ginzton, I. R. Nielsen, and S. Sonkin, Design and Performance of a High-Power Pulsed Klystron, Proc. I.R.E.. 41, 1595 (November, 1953).

35. M. B. Knight, Practical Analysis of Vertical Deflection Circuits, Tele-Tech, 12, 62 (July, 1953).

M.iGNETIC AMPLIFIERS

36. A. V. Lamm, Some Fundamentals of a Theory of the Transductor or Magnetic Amplifier, Trans. AIEE, 66, 1078 (1947).

37. E. L, Harder and W. F. Horton, Response Time of Magnetic Amplifiers, Trans. AIEE, 69, 1130 (1950).

38. A. I. Pressman and J. P. Blewett, A 300 to 4000 Kilocycle Electrically Tuned Oscillator, Ргж. I.R.E., 39, 74 (Januaiy, 1951).

39. James G. Miles, Bibliography of Magnetic; Dcvice. and the Saturable Reactor Art, Trans. AIEE, 70, 2104 (1951) (containing a list of 901 references).

40. H. L. Durand, L. A. Finzi, and G. F. Pittinan, Jr., The Effective Ratio of Magnetic Amphfiers, Trans. AIEE, 71, 157 (April, 1952).

41. H. W. Lord. Dynamic Hysteresis Loops of Several Core Materials Employed in Magnetic Amplifiers, Trans. AIEE, 72, 85 (1953).

42. S. B. Batdorf and W. N. Johnson, An Instabihty of Self-Saturating Magnetic Amplifiers Using Rectangular Loop Core Materials, Trans. AIEE, 72, 223 (1953).

43. W. A. Geyger, Magnetic Amplifier Circuits, McGraw-Hill Book Co., New York, 1954.

44. R. W. Roberts, Magnetic Characteristics Pertinent to the Operation of Cores in Self-Saturating Magnetic Amplifiers, Trans. AIEE, 73, 682 (1954).

45. H. F. Storm, Magnetic Amplifiers, John Wiley & Sons, New York, 1955 (contains exten.sive bibliography).

tb.4nsf0rmek standards

46. ASA, American Standards for Transformers, Regulators, and Reactors C57.22-1948.

47. NEMA, Standards for Transformers, No. 48-132.

48. AIEE Standards; No. 1. General Principles Upon Which Temperature Limits Are Based. No. 551. Master Test Code for Temperature Measurement. Progress Report of AIEE Magnetic Amplifier Subcommittee, Trans. AIEE, 70, 445 (1951).

49. RETMA Standards: Power Transformers for Radio Transmitters TR-102-B. Power Filter Reactors for Radio Transmitters TR-llO-B. Audio Transformers for Radio Transmitters TR-121. Audio reactors TR-122. Iron-Core Charging Reactors TR-127. Pulse Transformers for Radar Equipment TR-129.

general

50. D. S. Stephens, Lightweight Aircraft Transformers, Trans. AIEE, 68, 1073 (1949).

51. P. G. Sulzer, Stable Electronic Voltage Regulator, Electronics, 23, 162 (December, 1950).

52. W. D. Cockrell, Industrial Electronic Control, McGraw-Hill Book Co., New York, 2nd ed., 1950.

53. R. E. Collin, Theory and Design of Wide-Band Multisection Quarter-Wave Transformers, Proc. LR.E.., 43, 179 (February, 1955).

INDEX

Air gap, see Core gap Air-core transformer, 224

resonant peaks, 227

tuned, 226 Aircraft power supplies, 30, 80 Alternate stacking, 98 A-c grid voltage, thyratron, 239 A-c resistance, 106, 220 Ambient temperature, 53, 107, 290 Ampere-turns, 13, 208, 248

per inch, 90, 262, 269 Amplification factor (ц), 141, 144, 182

variations in, 256 Amplifiers, 140

bistable, 270

classes, 142, 163, 182, 200, 212, 215, 236

constant output, 257

efficiency, 143

equivalent circuit, 141

frequency response, 147, 175, 179, 194,

214, 222, 305 load line, 157, 264 magnetic, 259 phase angle, 155, 179, 194 plate resistance, 141, 160, 168, 182, 298 potentials, 140 power output, 143, 264 pulse, 3, 294

push-pull, 143, 163, 175, 193, 200, 209, 282

reactive load, 155, 194 sawtooth, 339 self-saturated, 273 stability, 179, 209, 270, 290 tests, 208

transformer-coupled, 141, 170, 176,

214, 294 tuned, 142, 216, 226, 235 turns ratio, 141, 147, 152, 170, 176,

258, 266, 268, 282, 295, 302 voltage gain, 145, 176, 178, 202 voltage ratio, 149, 152, 211, 285 voltages, 141, 157, 194 Amplitude-modulated wave, 255

Angular frequency, 6, 67, 114, 118, 276, 302

Anode, see also entries beginning with Plate

Anode characteristics, 155, 169 Anode current cut-off, 140, 256

in class В and С amplifiers, 142 Anode transformer, center tap, 75

currents, 74

design, 77, 82

800-cycle, 82

leakage inductance, 74

secondary voltage, 75 Anode windings, rectifier, 63 Apparent permeability, 308 Artificial fine, 186, 196 Attenuation, 117, 145, 227

wave filter, 182 Audio transformers, see Amplifiers Automatic gain control, 256 Automatic volume control (AVC), 258 Autotransformer, 250

pulse, 312

variable, 251 Average current, 15

rectifier, 64

Backsлving voltage, 299, 320, 330, 333, 340, 342

Balance in З-рЬазе transformers, 118, 126

Band width, 186, 224, 226

Bank winding, 214

Beam tube, 168, 199

Bias, magnetic amplifier, 275

Bleeder load, 125, 134

Blocking oscillator, 329

Breakdown voltage, 43

Bridge-type rectifiers, 62, 75, 113, 278

Butt stacking, 99

Bypass capacitance, 197, 212, 219, 243

Calculation form, anode transformers, 80

filament transformers, 71 Calorimeter, 313

Capacitance, air-core transformer, 226