This two-transistor circuit is from a December 1964 Radio Electronics. Modern transistors can be tested. The headphone must be high impedance or crystal with a 2k2 resistor in parallel.
This well-known configuration of the guitar effects pedal was obtained in an English magazine from...
This circuit was obtained in the National Semiconductor Linear Applications Handbook of 1994. The...
For -48 V voltages, this fast sensor was found in a 2005 Linear Technology application manual. The...