The Amplifier hall be single channel with an input gain control and an output Level Meter on the front panel. The Amplifier hall accommodate an unbalanced high impedance input, or a balanced low impedance input with an optional Plug-In accessory transformer. The Amplifier hall be capable of delivering a minimum of 60 W, continuous sine wave, 20 Hz-20 kHz, into a 4 Q load 6007 The Amplifier hall incorporate an output transformer allowing full power operation, 35 Hz-20 kHz, into an 8 Cl, 16 Cl or 70.7 V line as well as a direct output terminal for a 4 O load.) [6008: No output transformer and only a direct output terminal shall be provided, but it shall be possible to install an output transformer easily at any time.) The Amplifier hall have < 0.2% THD, 20 Hz-20 kHz, @ 60 W, direct output 6007 The Amplifier hall have < 0.2% THD, 35 Hz-20 kHz, @ 60 W, transformer output.) Frequency response shall be ± 0.5 dB, 20 Hz-20 kHz, @ 1 W. Power bandwidth shall be 10 Hz-40 kHz. Construction of the Amplifier hall be modular. The entire Amplifier circuit, except for the Power Supply 6007 and output transformer) shall be mounted on a single circuit board attached to the heat sink, which assembly shall be removable from the unit with the mainframe still mounted in a rack. Cables connecting the circuit board to the mainframe shall be of a length sufficient to allow removal of the board without disconnection and shall disconnect easily at two plugs. The Amplifier hall occupy three standard EIA rack spaces and shall operate on 120/240 V AC, 50/60 Hz.