Radio with amplifier (CB20486E)

We found this circuit in a publication of 1991. The audio amplifier is an operational that admits equivalent.

Battery Low Indicator (CB4796E)
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
Photodiode Amplifier (CB905E)
The gain for this circuit is given by the ratio between R2 and R1. The circuit is suggested by...
Commercial Reflex Receiver (CB958E)
Only for reference this is a circuito f a commercial receiver of the year 1958. The circuit uses...