The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
This circuit is from a Harris Semiconductor datasheet from the 80s. However the circuit can be...
August 2016 - It can be obtained from Mouser Electronics the new clock buffers HMC7043 of Analog...
An interesting option is the one that makes use of the MC3373 integrated circuit and which is...