This variable frequency circuit was found in a Popular Electronics from the 90s. The circuit outputs to a small speaker and can be powered by voltages as low as 3 V.
In the figure we have a bridged circuit for the use of an SCR in a full wave control. The diodes...
This configuration found in other companies' manuals is from Motorola's 1993 Linear Interface ICs....
The figure shows how to use a 3-winding transformer to switch outputs with different voltages by...