Wattage Testing
Douglas as Guitars and Amps
Aug|1|2009
So I was getting used to my new audio generator today by test the output power of my various amp builds. The generator is much nicer than hooking up a laptop and balancing it on top of one’s scope.
I used a 1k sine wave and a 100 watt 8 ohm dummy load with a true RMS multimeter across the load. I also measured the resistance of the dummy load while it was warm after the test. The heat causes the resistance to rise slightly
Here are my findings.
Spitfire build – 12 watts (P/P EL-84, cathode bias, EZ81 recto)
B-18 build – 40 watts (P/P 7027, fixed bias, 5AR4 recto)
Micro AA764 – 2 watts (SE 6AQ5, cathode bias, SS recto)
Now my numbers are pretty conservative because I was looking for the clean output. I didn’t allow the crossover notch to appear in the sine wave when I did my test.
Maximum output was,
Spitfire – 21 watts
B-18 – 105 watts?!
AA764 – 3.5 watts
This was the point where things were horribly distorted and the scope had a grotesque looking square wave. Interestingly, the AA764 produced a beautiful square wave with the right input signal. It really is a high gain amp for your bedroom if you like the smooth overdrive of a 6V6-family tube.