http://www.gammaelectronics.xyz/audio_01-1977_bgw.html
I can only get sound when I plug the into the EQ or tape inputs. Then, I can only use the gain on the amps to adjust the volume.You have to connect the crossover and power amps to the main output, make sure the jumpers on "ext. equalizer" are in place.
There are two buttons in the power area that say "power" and "amp". Never had a preamp that had 2 buttons in this area before.According to the Block diagram the "amp" switch is control the "pwr amp" outlet on the back panel.