The indicated circuit uses an unusual buffer from National Semiconductor. The frequency is given by resistors R1 and R2 as well as capacitors C1 and C2.
This small converter using Only one transistor was published in the Radio Electronics magazine from...
This circuit was found in a Popular Electronics of the 1990s. Its purpose is to expand the scale of...
This receiver was found in old English documentation and any general purpose NPN transistor can be...