1、/- I - Audio Transformers for Electronic Equipment o ;i( F 8 H m 4 c RS-174 (Revision of TR-121) e e December 1956; Engineering Department RADIO- ELECTRONICS - TELEVISION MANUFACTURERS ASSQCIATION L EIA I174 56 W 3234600 0028502 T W ?. 1 RETMA shndards are adopted in the public interest and are desi
2、gned to eliminate mrsunder- standings between the manufacturer and the purchaser and to assist the purchaser in .selecting and obtaining without delay the proper product for its particular need. Existence of such stand- ards does not in any respect preclude any member or non-member of RETMA from man
3、ufacturing or selling products not conforming to the standard. Any proposal of recommended standards and practices made by the Association is without any regard to whether or not their adoption may in any way involve patents on articles, materials or processes. By suck action, the Association does n
4、ot assume any liability to any patent owner, nor does it assume aiiy obligation whatever to parties adopting the recommended standards or practices. Published by Engineering Department 2001 Eye Street, Ne We, Washington, D. C. 20QOQ PRICE $1. 80 - - .- LI Printad IR U.8.A. EIA 174 56 m 3234600 00285
5、03 1 m RS-174 Page 1 AUDIO TRANSFORMERS FOR ELECTRONIC EQUIPMENT (Front Standards Proposcil No. 512 formulated under the cognizance of RETIGIA Engineering Committee SQ-4 on Transformers and Reactors) 1. SCOPE This standard covers iron core transformers for use in Electronic Equipment in which long l
6、ife, reliability and continuity of operation are essential, and which are required to transform voltages with fidelity over a designated frequency band and operate between specified impedances. It is not intended that the “frequency band” referred to above be limited to the region of audible frequen
7、cies. 2. DEFINITIONS 2.1 Electrical terms used in this specification shall be in accordance with those given in “Ameri- can Standard Definitions of Electrical Terms.” AS-A No. C42-1941, except as otherwise noted. Reference is made to the following ASA definitions: 65.10.005 Audio Frequency 65.10.015
8、 Frequency Band 65.10.020 Band Width 65.10.025 Fundamental Frequency 65.10.030 Harmonic 65.10.300 Modulation 65.11.010 Decibel 65.11.020 Power Level 65.11.035 65.11.430 Distortion 65.11.440 Non-Linear Distortion 65.11.450 Fidelity 65.11.500 Self Impedance Insertion Loss (or later revision) 2.2 The R
9、MS working voltage between any winding and any other winding or ground, shall be defined as 0.707 times the sum of the maximum dc voltage and the peak ac voltage which may appear between that winding and the other winding or ground under normal conditions of con- tinuous operation. 2.3 dbm is define
10、d as db referred to one milliwatt, sine wave, single frequency. 2.4 Frequency response is defined as the ratio of the secondary voltage over the specified fre- quency band to the secondary voltage at the mid-band frequency, or any arbitrary reference fre- quency, with the source voltage held constan
11、t. In the case of modulation and driver transformers the load voltage may be held constant. In such cases the frequency response will then be defined as the ratio of the source voltage over the specified frequency band to the source voltage at the reference frequency. 2.5 Reflected impedance is defi
12、ned as the impedance presented to the source by the transformer over the specified frequency band, all secondary windings being loaded as specified. The desired value of impedance should be given with tolerances. 2.6 Efficiency is defined in several ways : 2.6.1 Overall efficiency is the ratio of th
13、e power delivered to the load, to the power delivered to the transformer, and is expressed in percent. 2.6.2 Copper efficiency is the ratio of the power supplied to the secondary load or loads to the sum of that power and power losses in the conductors comprising the secondary and primary windings,
14、as distinguished from losses in the magnetic and other aspects of the transformer structure. NOTE: Overall efficiency, an important characteristic of power transformers, is used in rela- tively few instances as a measure of quality for audio transformers. 2.7 Longitudinal balance is the ratio of tra
15、nsmission of a signal introduced transversely to the transmission of a signal introduced longitudinally with the voltages from lines to ground held constant and equal. The balance must be stated for all combinations of connections taken over Y EIA i174 56 3234600 0028504 3 1 RS-174 Page 2 the assign
16、ed frequency band. Balance shall be expressed in db. Refer to Fig, 2, Appendix III, for illustrative circuit. 2.8 The termination of a transformer winding is the total impedance of the circuit connected to the winding. NOTE: While terminating impedances are frequently the source and load impedances,
17、 such is not always the case since the termination may include other network components which might be used between the transformer and its source or load. 2.9 The mid-band frequency is defined as the square root of the product of the lowest and highest frequencies in the specified bandwidth. 3. PUR
18、CHASE SPECIFICATION The purchaser will specify : 3.1 Electrical Requirements 3.1.1 The source and load impedances in ohms, preferably chosen from standard values in Appendix I. (a) If any of the source and load impedances are more than 5% reactive at any frequency within the specified frequency band
19、 the purchaser shall dene the reactance-frequency char- acteristics. It may be necessary to specify these characteristics over a broader frequency band than that specified in 3.1.4. (b) The tube type with specific operating conditions and voltages or an accurate description of the source and load wi
20、th associated circuits. 3.1.2 The reflected impedance at specified frequencies and voltages. 3.1.3 The dc voltage and direction and magnitude of direct current in each winding, and the anticipated variation thereof, 3.1.4 The frequency response required and the permissible deviations thereof with re
21、spect to power level. (a) If desired, instead of frequency response, the highest and lowest frequencies to be trans- mitted, the open circuit inductance of any winding at a specified low frequency ac voltage and rated dc, and any leakage inductance of interest, may be specified. 3.1.5 The power to b
22、e delivered to each load impedance over the frequency band specified in 3.1.4, the upper and lower limits to be specified in watts or dbm. Unless otherwise specified the lower limit shall be taken as 20 db below the upper limit for test purposes. 3.1.6 The minimum overall efficiency at the power spe
23、cified in 3.1.5, if desired. NOTE: In cases where core loss is not of importance and unless otherwise specified, the qualifi- cations and determination in 5.1.3 (b) shall apply. 3.1.7 The minimum longitudinal balance permissible between halves of windings terminated with balanced impedances. This ba
24、lance may be expressed in db at the highest and lowest fre- quencies specified in 3.1.4. In the case of push-pull primaries, the voltage and impedance balance should be specified. In Class B Modulation transformers, the balance of the leakage reactance of each half of the primarp to the secondary wi
25、nding is of importance. 3.1.8 The maximum permissible harmonic distortion over the frequency band at the maximum power specified in 3.1.5 expressed in percent of the total output voltage of the fundamental frequency, measured as specified hereafter in 5.1.7. 3.1.9 Electrostatic shielding if required
26、. 3.1.10 If magnetic shielding is required, the maximum pick-up in volts for the specified windin , at a specified low frequency and maximum field strength, measured as specified hereafter in 5.1. f . 3.1.11 Any significant operating requirement not treated above, such as unusual surge voltage resul
27、ting from power supply fault, keying or switching. EIA 174 5b E 3234600 0028505 5 E RS-174 Page 3 3.2 Construction 3.2.1 General Assem or (b) Shall, where (a) is impracticable, be induced in the winding under test ; while in either case, other windings and core are grounded. (a) On first measurement
28、 be less than the following limiting values 8.1.4 The magnitude of the corona level across insulation subject to damage by corona shall RMS Worlcing Voltage (Kilovolts) Corona Level (Microvolts) e Up to 8.6 1,000 8.61 to 15 2,600 (b) On second or repeated measurement, shall be less than twice the ab
29、ove stated limiting values. Appendix I The following table shall be standard for specifying impedance values to be used for transformer terminations : 4 ohms 8 ohms 16 ohms 38 ohms 150 ohms 600 ohms 2,400 ohms 9,600 ohms 40,000 ohms 100,000 ohms Appendix II LOAD TEST 1. The load for each seconclary
30、winding shall be an impedance having the value specified in 3.1.1. 2. The transformer shall be loaded at the maximum output epecified in 3.1.6, with dc current speci- fied in 3.1.3, and duty cycle specified in 8.3.3. a US-1 74 Poge 8 3. 4. 5. 6. 7. 0. 9. EIA 174 56 3234b00 0028510 9 T If connections
31、 are provided for more than one source voltage, the lowest voltage full capacity tap shall be used for test. The thermometer for measuring the ambient temperature shall be protected against trivial temperature changes by means of an oil bath or other suitable material. 4 The thermometer for measurin
32、g the temperature of the core or case shall be secured in contact with the surface to be measured by means of glaziers putty or other suitable device. The transformer under test shall be protected from air drafts and radiation from warmer objects. The test may be performed at room temperature. The l
33、oad test shall continue.unti1 the temperature of the transformer core or case shows constancy for three successive readings at intervals of at least 30 minutes. The temperature of the primary and secondary windings shall be computed (for copper) by the resistance method using the following formula (
34、A.I.E.E. Rule 13-207) : R r T = - (234.5 + t) - 234.5 t = reference temperature in “C. of winding. T = temperature in OC. of winding to be calculated. r = resistance in ohms at reference temperature t. R = observed resistance in ohms at temperature T. In applying this method, the resistance (r) at r
35、eference temperature (t) shall be measured after conditioning the transformer for at least eight hours in a location free from drafts and until three successive temperature readings of the ambient and core or case, taken at 30 minute intervals, are constant ; and this constant temperature shall be t
36、he reference temperature (t) . The observed resistance (R) shall be measured as soon as practicable and within 15 seconds after the comple- tion of the test run on transformers weighing less than 10 pounds. The resistances of the wind- ings having the higher temperature shall be measured first. 4 10
37、. The temperature rise of the transformer shall be computed by subtracting the temperature of the ambient air around the transformer at the end of the test from the temperature of the hottest winding or of the core (whichever is higher) at the end of the test. Appendix III The test circuit shown in
38、Fig. 2 shall be used where applicable for determining balance in trans- former windings with reference to 2.7 and 3.1.7. The resistors Rt and R? should be of the precision type and of equal value. The source terminals should deliver to the transformer a voltage which has less unbalance by at least 1
39、0 db than the value specified in 3.1.7 as defined by 2.7 at any frequency within the frequency band specified in 3.1.4. The resistors shall be non-inductive within the frequency limits specified above, and the sum of the values of Ri and Rn shall be equal within 5% to the terminating impedance speci
40、fied for the winding used as the source winding. This test may be used in conjunction with that specified in 6.1.6 to determine compliance of the transformer with 3.1.7. Test may be made at any frequency but 1000 cycles shall be used unless another frequency is specified. In general at the low frequ
41、encies, the element contributing to unbal- ance will usually be winding resistance and turns; in the middle frequencies, winding turns; and at the high frequencies leakage inductances and winding capacitance. An oscilloscope may be u?ed if the relative phase of the secondary voltage is of interest. The test is not limited to two-winding transformers and the test circuit may be modified as required. EIA 174 56 m 3234600 0028511 O m RS- 174 Page 9 - - STEP I- LONGITUDINAL VQLTAGE *2 STEP 2- TRANSVERSE VOLTAGE LONGITUDINAL BALANCE = 20 log 5 db. =, FIG. 2
