This is a two stage, two channel (pre-and post gain adjustable) battery powered tube pre-amplifier. Microphones or other sources can be plugged into this unit. It is very portable and easy to use. This unit runs on 8 AA batteries and should last anywhere from 2 to 4 hours. It has an internal high voltage power supply that is regulated to 80 volts or so using zener diodes. I have received many inquires asking for the schematic to this pre-amp. This is built out of a pair of 12AX7’s (West German ‘Computer Tubes’) and an HV supply made out of a 555 timer, a TDA series 2 Watt audio amp chip, and an old military surplus audio transformer (see grey can on top of chassis).