Transistor PP amplifier for reception and modulation
For a long time push-pull type LF amplifiers with transformers mostly was been used in radio equipment. The output quality is limited by the characteristics of the transformers. When it comes to the transmission of voice signals in radio equipment, this is not necessarily a disadvantage. The quality is sufficient here in any case and the narrowed frequency range may even be advantageous for speech clarity. Another positive feature is the good efficiency, which can be particularly favorable in battery operation.
Therefore I have used the circuit shown often in a slightly modified form for self-built devices. Suitable transformers one can win by exploiting obsolete Japanese radios or two-way radios. If the output transformer provided with an additional modulation winding, one can use the circuit in self-built radios as a modulation amplifier, by suitable switching over for transmitting. For receiving operation, the circuit amplifies enough for loud speaker reception, if it is connected on the input side via the volume control directly to a standard AM diode demodulator. For other demodulators, e.g. for FM or SSB, interposing a pre-amp may be necessary for sufficient loud output.