MCINTOSH - 50W-1 - Mono Amplifier - Schematic Diagram 电路图 维修手册.pdf

ly larger totul loss i nthe larger core. It would be well to joint out at this time that for 6 L G tubes operated in Class A B or Class B, the ratio of inductive reac tance of the primary of the output transformer to the leakage reactance between the primaries must be 80,000 to one or greater to permit 1 per cent dis tortion at 20 kes and full output to as low as 20 cps. From the above discussion it seem- impractical to reduce the leakage re actance sufficiently to permit high-efh- eiency ojeration and the only hope, therefore, is to go back to a conven tional Class A arrangement where : discontinuity in the current drawn ! each of the tubes does not occur over the operating cycle. The solution i shown connected to the associated cathodes. The solid jjosition of primary 2 is shown adjacent to primary 1 and this illustrates the first step in the de velopment of the unity coupled ampli fier. These two primaries are wound Fig. 8. E q u i v a l e n t circuit simplified f r o m F i g . 7. together in a bifilar manner as if they were one winding and. therefore, there is between them both a capacitance coupling turn by turn, and a magnetic coupling due to the presence of the com mon core. Since the wires occupy prac tically the same space, the coupling is exceedingly high and measurements show that it i- practicule to wind coils with a ratio of primary inductance to leakage reactance much better than 2000,000 to 1. This, therefore, provides a way to eliminate the leakage reactance which in conventional transformers far exceeds the minimum ratio requirement of 80,000 to 1. W e now, therefore, have a system which appears to have promise by reason of finding a way to eliminate the leakage reactance between the pri mary windings which in turn removes the barrier which has blocked for so many years the use of high- efficiency circuits in high quality audio amplifiers. It is obvious that other varations of approach have been considered which accomplish the desired purpose to some extent at least, such as winding the two primaries on a common core not hifilarly and utilizing a suitable capacitance for couping the ends of these windings so as to maintain the TWO windings at proper and identical a.c. potentials. One advantage of the bifilar winding is, of course, a reduc tion of the number of components re quired, and it sidesteps some of the dif ficulties which grow out of the use of alternate approaches. It may also be obvious here that since the two primary windings are unity coupled there is no longer any need for sectionalizing the primary as is common in high quality transformers today. This results in an economy in manufacture. Circuit Arrangement To make Fig. 5 a practical circuit, the cathodes are connected to one coil and the plates to the other coil without changing their osition in the circuit from an a.c. standjoint hut permitting AUDIO ENGINEERING F i g . 9. S c h e m a t i c of M c i n t o s h 5 0 W - I amplifier. DECEMBER, 1949 RadioFans.CN 收音机爱 好者资料库