amplifier_30wpp.pdf - POWER AMPLIFIERS with valves an approach and a practical circuit � by Claus Byrith 1 1 INTRODUCTION A couple of years ago I met

amplifier_30wpp.pdf - POWER AMPLIFIERS with valves an...

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POWER AMPLIFIERSwith valvesbyClaus Byrithan approach anda practical circuit
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21. INTRODUCTIONA couple of years ago I met Per Lundahl of the Swedish company Lundahl Transformers and hisfather at an exhibition in connection with an Audio engineering Society Convention, and I triedto persuade him to make me a pair of output transformers with some additional secondaries forexperiments, I wished to conduct. He was not enthusiastic, but we had a fine conversation,nevertheless, about valve amplifiers, of course. After some time, I said to him that if he wouldfulfil my wishes, I would supply him with a paper concerning the matter and a practical con-struction that could be built by amateurs, resulting in a 30 W amplifier where high quality goeshand-in-hand with simplicity and modest costs. To make a long story short he agreed, and here Iam left to keep my promise, and I am beginning to realise that despite the fact that the matter isstraightforward, it is not easy to pass yesterday’s knowledge on to the audio enthusiast of todayin a short, simple, digestible and yet satisfactory way, but I shall try my very best. I am oldenough to have experienced the evolution of valve amplifiers since the mid fifties but am, atleast so I am told, still in full command of my faculties.The last decade has seen a growing interest in valve amplifiers, which is not only due tonostalgia but more to the fact that a good valve amplifier sounds different from most solid stateamplifiers, and despite the fact that the measured performance cannot compete with modernamplifiers, they sound very good and they do not expose you to the same degree of listeningfatigue as many solid state amplifiers, truly or falsely!, are accused of. I shall not try to describethe sound. The fact that you have got so far in this paper indicates that you understand what I amtalking about.Often involved in discussions about this topic, I am forced to realise that much of the know-ledge that was common goods 40 years ago has disappeared and what remains is a conglomerateof distorted facts and a complete lack of understanding of how these facts are interlinked and oftheir relative importance. It is as if it were seen in a distorting mirror in the hall of mirrors in anamusement park. Parts of the image are magnified out of all proportion and other parts of maybeeven greater importance are simply not there!I shall now try to improve your understanding.
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32. THE LAYOUT AND THE BUILDING BLOCKSA push pull valve amplifier almost invariably follows one of the two schemes shown in blockdiagrams below:Very few designs differing from these two have proven fit for real life, the Quad II being anotable exception (you will find the diagram in the appendix together with a brief explanation).
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