This single trigger circuit has been indicated for photography applications. The circuit is from a 1964 Electronics World. The transistor is general-purpose and the SCR can be of any type.
Found in old documentation, this simple test checks both the polarity and the existence of voltage...
Found in Radio Electronics from the 90s, this circuit can vary the frequency in small values...
This circuit can be made usng the TIP32 transistor but must use carbon microphone (not very common these...