Calculating Gain of Transformer Couple Transistor Amplifier

Thread Starter


Joined May 9, 2020
Hi all,
I was working on an old AM radio and I started wondering how you could calculate the gain of a true common-emitter BJT whose collector was connected to an IF transformer (turns ratio 57/7). The impedance seen by the secondary is about 2K so primary impedance should be roughly 49K ohms. Anyone know the formula or a procedure?


Joined Apr 17, 2019
Approx : Rc/ (re+Re). The emitter is bypassed? Rc is primary impedance

Also, please why is the primary impedance 49k?

sparky 1

Joined Nov 3, 2018
This page has a Block diagram of a superheterodyne receiver
The IF amplifier sometimes 455 kHz the primary can be tapped might include a parallel capacitor.
The IF transformer having different configurations. Narrow it down either schematic or more information. yellow dot, part number, size
Maybe this radio is earlier and not have a standard IF at all. Early radios had moveable coil adjustment.
Possibly it will be easier like one of these:
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