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.

RS232 temperature interface (CB21278E)
Found in an Electronic Design from the 90's, this circuit uses common components. The circuit is...
Locked Light Relay (CB3868E)
When the sensor receives light, the relay closes its contacts and remains so even after the light...
90V Pulser (CB8838E)
This circuit produces pulses of 90 V at intervals that can reach 5 minutes. The circuit is from a...