You don't want to run any speaker(s) with less impedance than the stock special celestion with 8 Ohms impedance. If you burn your amp, it's done, and they don't make spider jam's anymore. That being said, if you run a cab(s) with more than 8 Ohms, that's the safest. If you run 16 Ohms for example, 2 x 8 Ohm speakers or cabs in series it will thin out the sound and you'll get less than 75W output reducing any chance of doing harm to the Amp.