This small 4-tube amplifier, one of which is a full-wave rectifier, was found in a 1941 publication. The circuit has a speaker output and can be used as a sound box for ambient sound. The power is a few watts.

This small 4-tube amplifier, one of which is a full-wave rectifier, was found in a 1941 publication. The circuit has a speaker output and can be used as a sound box for ambient sound. The power is a few watts.