[Vintage-Audio] how to calculate RMS power

[rick]

Since I just calculated RMS power on a homebrewed guitar amp, this is 
fresh in my mind.  I'll let smarter people than me to answer Duane's 
questions.

measure the peak to peak voltage at max output before clipping
divide by two to measure peak voltage - since it half is above and half 
is below
multiple by the square root of 2 to get RMS
Vrms squared divided by the speaker load equals watts RMS

example is my amp (single ended 6v6gt) measured 14.8 volts peak to peak 
with an 8 ohm speaker.

14.8/2 = 7.4
7.4 * 0.7 = 5.2 volts rms
5.2*5.2/8 = 3.4 watts rms

my little amp puts out about 3.4watts.

rick