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 was obtained from an old American documentation having a limited adjustment range....
This 555 timed touch switch was found in a 90s Hands-On Electronics. It triggers a buzzer, but a...
The transistors of this old circuit from the 60s can be the BC548, in a current version. The...