Brucie, as some of the previous replies indicated, the wattage specified on the back panel is nothing to be concerned about(although on some other boards I've read almost hysterical discussions on the point). Two rating groups(EIA/CEA and FTC)require a preconditioning period of 1/2-1 hour at 1/8th(considered to be roughly the average level below maximum on CDs)of full rated power before testing begins. The amp is then required to supply full rated power for 5 minutes(all channels simultaneously, FTC;one channel at a time full power with others at 1/8th power, EIA/CEA). Most manufacturers measure the power consumption at the 1/8th point and put this on the back as an indication of the average(not maximum)the amp uses when in operation. Since the overall efficiency of typical amps is no more than 50% at maximum power and drops at lower levels(possibly 20-25% at 1/8th), your 260 watt figure computes. 5X100= 500 watts, but at 1/8th power is about 63 watts output, which at about 25% efficiency would require about 252 watts of power consumption averaged over the whole CD.
So, the bottom line is that while the power consumption number on the back might help you to estimate the electric bill, it doesn't describe the maximum capabilities of the amp.
