What is cathode biased….the circuit that your tech built?I had it converted to a sort of Fender Bandmaster circuit 14 years ago, the tech who did recommended gutting it instead of bringing up to quirky original specs which wasn't terribly well suited for bass to begin with. Two channels; Volume, Treble and Bass controls. If I remember, the transformers are rather wimpy but that contributes to it's saggy, somewhat rich midrange sound. Cathode biased too, which sounds like it has a tube rectifier even though it's solid state rectified.
Both the GA100 and GA200 are fixed biased outputs.