RF or even switching transistors like the 2N2222 can be used in this circuit. The capacitors are ceramic and the frequency is determined by the crystal.
This circuit source a voltage proportional to the number of the input pulses. The circuit has a...
This circuit is from a 90's Radio Electronics. The circuit operates accurately up to about 15 kHz...
This is a circuit suggested by Linear Technology in a 1980s documentation. The integrated circuit is from...