This circuit is from an old Mullard (Philips) manual with applications using the 555. Choosing appropriately the resistors and the timing capacitors, the ranges obtained can exceed days.
The operational amplifier of this balanced circuit is old and can, however, be implemented with...
This SSB modulator does not use the balancer transformer. The circuit is from an 80's...
In the figure we show a configuration for a crystal controlled overtone oscillator using a...