This circuit is from a 60's documentation. The capacitance C1 can be between 20 pF and 0.01 uF depending on the generated frequency. Equivalent transistors may be employed.
This circuit was obtained in an old documentation, but it is still current by the used components....
This circuit makes use of a transconductance operational amplifier. It generates signals with TTL...
This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer...