I pulled the power tubes from a 61 twin and installed two Yellow Jackets. Taking the power tubes from 4 each to two creates an impedance mismatch with speakers. To compensate I put two Celestion Silver Alnico speakers in the cabinet. The net result is a two channeled 15-18 watt amp with 30 watts of alnico speakers. The perfect marriage of Fender Twin and AC-15 Twin. Truly a great sound!