Vince, one slight correction: dB are always 10 but never 20 times the common logarithm of the numbers in question, so the difference dB difference between a 200 watt amplifier and a 100 watt amplifier would be, as you state, 10 log 200 - 10 log 100 = (10 x 2.30103) - (10 x 2.00000) = 23 - 20 = 3 dB.