These are a pair of Cary Audio 805 Reference Series (CAD-805RS) with 211/845 switch selector. Can use 845 or 211 output tubes. Ability to dial in feedback allows for continuous control across the spectrum, from romantically "warm" and "musical" to ultra-linear and dynamic. The audio signal from the 300B interstage transformer will drive the 211/845 output tube to 50 watts Class A2, with the first 27 watts in Class A. The owner's manual states that a home electrical system that has a ground Ioop will cause the amplifiers to hum slightly (not audible from the sitting position). The manual states that the hum is eliminated with a 2-pin adapter on AC cord to float the ground. I have all original packaging material and owner’s manual. These amplifiers are in brand new condition with less than 100 hours on them. I am the original owner with no pets, and smoke-free environment.