Quote:
Originally Posted by Synchrodyne
Where output transformers were used in small transistor amplifiers (non-hi fi) in radio receivers and record players, my understanding is that it was not normal to take feedback (if used at all) from the output transformer secondary, but rather from one or other of the output transistors.
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Yes that is right. The only radio I have with this technique in my entire collection is the unique and interesting NZ made Pacemaker radio from 1957, check out the schematic (figure 5) on page 9 of this article on it, the feedback taken from one output transistor. I had to transcribe the schematic from the radio. The audio circuit is interesting in many other ways too, with a direct coupled pre driver and driver and the bias for the opt stage derived from the driver emitter circuit . The pre driver transistor is used an an output transistor temp compensation device!
http://worldphaco.com/uploads/THE_PA..._FROM_1957.pdf
(Also this radio has been said to be one of the very first transistor MW band radios with an RF stage).