I found this circuit in an old Argentine publication from 1973. The components are no longer easily found, as the transistors are made of germanium. However, the circuit can be changed to silicon transistors, transformers being the critical components. The circuit must use a carbon microphone and the power must come from large batteries or cells. The speaker must be of high performance. Component values can be approximated to current standards. The circuit serves more as a reference for equipment restoration.
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