Circuit 4-1 is a single stage amplifier with a double tuned input transformer and a single tuned output transformer. The double tuned input transformer, T1, is designed to provide the proper load (100K) for the mixer or converter. The secondary of T1 is tapped to provide the proper mismatch to the input of the i.f. transistor 2N373 for stability considerations.
The single tuned transformer T2 has a tapped primary, such that the proper load is established for the output of the i.f. transistor and in turn provides the mismatch necessary for stability. The total mismatch (16.5 dB) in both the input and output of the transistor combined provides a maximum usable gain of 37.5 dB.
The turns ratio, tap to secondary, is established so that the reflected inpedance of the detector in parallel with the tuned resistors of the primary at the tap provides the proper load for the i.f. transistor. A 180° phase shift is provided in the transformer T2 by a reversal of the secondary. This is necessary to provide a means of neutralization by means of capacitor C9, which couples a signal equal and opposite in phase to the signal which is inherently coupled from output to input through the internal feedback capacity of the transistor, thus providing neutralization.
A simple straightforward AGC system is included. With no signal applied to the amplifier, the base of the transistor, and the junction of R4 and R5, are negative and the emitter current is at its quiescent value of about 1 mAdc. As the input signal to the amplifier increases, the detected signal makes the junction point of R4 and R5 go positive. Thus the base bias voltage, the emitter current, and the gain of the stage will decrease.
Reference: pages 4-20, 4-21, MIL-HDBK-215, 15 June 1960
Reference: page 36, RCA Semiconductor Products, 1960
Reference: page 30, RCA Semiconductor Products, 1960