This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
When the supply is established, the load only receives the supply some seconds later, a time that...
With S1 closed, when dark, the triac will supply the load with the power set in R4. The LDR is...
This interesting amplifier for frame antenna for the medium wave range was found in a Popular...