BillFitzmaurice.info

If an amp is rated for 2,4, and 8 ohms, will you harm it by running it at 16? Or running a 4 ohm amp at 8?

Running a higher impedance should not be a problem. There could be exceptions and I wasn't around during the hey day of large tube amps but a higher impedance load is usually OK. If you think about it, an open connector ( no load) has an extremely high (near infinite) impedance while a dead short has a zero impedance. Dead shorts and really low impedance loads cause more current to flow and can burn out parts or if you are lucky, only cause an amp to go into "protect" mode.

Tube amps are picky on the impedance. Solid state amps, the higher the impedance the happier they are, just don't go below the minimum or else they will overheat/over current and thermal out.