At the 1956 meeting of the society I described and demonstrated an OTL power amplifier that aroused much interest. Hundreds of audio fans built this amplifier and their satisfaction with its performance is attested to by their letters to me. Two deficiencies of this amplifier were its limited output (by today's standards), 18 watts which resulted in a direct current flowing through the voice coil of the loudspeaker when the output tubes had aged sufficiently to change their characteristics. These two drawbacks and the advant of stereo has led to the development of the present amplifier, described in this paper.
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