This circuit was found in a 90s Wels' Think Tank. The frequency depends on C2 and R3. The handset or speaker must be at least 80-ohm. Observe the low supply voltage.
This is stage is transformer coupled and was found in na old publication of the year 1958. The...
This circuit is from the magazine 73, for radio amateurs, from the 80s. The circuit uses common...
This indicator circuit used and game machines (arcades) to indicate that the machine is being...