Voltage amplifier with the 37 tube (T392E)

Found in a modern design book with tubes, this stage with the triode 37 has a plate current of 3.7 mA.

Shield for triac activation (CB7833E)
Found in Radio Electronics this circuit uses a fotodiac to drive a triac. The circuit can use...
Microphone preamp (CB22045E)
This circuit is from an old English documentation. It is intended for coupling a microphone to the...
Magic Spring (CB13041E)
Here is an interesting circuit to be used in physics demonstrations involving energy...