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20W two channel amplifier, with lineout, and a removal tone module to easily change the frequencies that the "HI/LO" switch accentuate or roll-off. tubes: 12AY7, 2x12AX7, 27C5(6V6), 5U4GB.
The circuit is largely based on a 1956-1960 Fender Pro 5E5-A circuit with a few exceptions: 7C5 are used instead of 6L6GC (the 7C5 is a 6V6 with a loktal base). Another variation is that one of the two channels is a AB763 "Blackface" preamp channel with 25K "Mid" control added.
The AB763 channel also has two tone shaping controls mounted on the bottom of the upper chassis, accessible via the rear cabinet opening. One is a "Slope" control switch that selects a slope resistor between 100κΩ, 55κΩ, and 33κΩ, and other switch is Cut switch that adds and removes a 25uf cathode bypass cap to the first gain stage.
The other channel has a single tone knob and a removable tone module that allows the capacitors on the "HI/LO" top mounted switch to be adjusted with major surgery to the circuit.
Of the two Speaker Jacks, one Jack is an extension jack that puts an extension speaker in parallel with the internal speaker, and other is an overide jack that allows the internal speaker to be switch off and only use an extension cabinet.
The Line Out jack allows a 150Ω output for recording or a PA console connection. The Level control attenuates the Line Out level to what +dB level is acceptable for the input device.
The Response switch selects a level of NFB (Negative feedback) for the power amp. "Flat" or "Normal" indicate a frequency response. "Open" removes negative feedback all together.