 There is no output impedance switch and the total impedance of the main plus external speaker has to be 4 ohms.In 1992 Fender introduced the '65 Reissue, with blackface cosmetics and circuitry, an output rating of 85W RMS and 8Ω Jensen C-12K speakers.The '65 Reissue is constructed with a printed circuit board and new 1/4" phone jacks for the footswitch pedal replacing the older RCA design of the vintage originals.