Nice working mono block using a push pull pair of EL-34 / 6CA7 output tubes. Likely assembled by someone who knew what they were doing. Quality components and oversize transformers that run very cool after hours of use. Preamp tubes are 6SN7 and a matched pair of GE NOS. The rectifier tube is 5U4 by RCA for Zenith. There is a pot on the deck to balance the output tubes with convenient 1/4" sockets that allow you to get across the precision resistors with your DC voltmeter. I've got these set 50/50. It sounds wonderful. Lots of power. Has an RCA connector input, so just plug in and hook your speakers to the 4, 8, or 16 ohm terminals reflecting the output transistor taps on the front of the chassis. Output tubes are Ruby and Mullard Russia - both at 92% on my meter so balanced. No hum from this amp. The power supply has been checked out and only cathode cap replaced as needed. This unit powers when plug is plugged to source. Intended for plugging into a preamp with powered outlets. Has an outlet on it for another amp if you want to do Stereo - diasy chained power will turn on both when this is turned on.  This is 25 lbs unboxed!