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.
This circuit from March 1984 Radio Electronics is intended to allow the use of an oscilloscope to measure...
The circuit in the figure uses the four current amplifiers of the LM3900 to generate a sawtooth signal...
This amplifier was found in a technical documentation from the 1970s. The circuit uses 2N2218...