This 6W amplifier with 4 tubes was indicated in an American documentation from 1947 to operate with recorders. The circuit uses a source with a transformer.
With this circuit we can activate a relay with a simple touch on the sensor. The relay can be 6 or...
This circuit was obtained in a 1979 publication. The operational amplifier is of the type with...
Found in a 1980s German publication, this circuit tests batteries by type. The circuit is based on a...