This circuit was obtained from a Philips documentation from 1968. The transistors can be replaced with equivalents, only with care so that the doubles are exchanged for matched pairs.
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in a 1990 Electronics World magazine. The circuit can be mounted today by...