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previous: SpeedRacer If memory serves (pls jump in here ... -- 2/21/1999 9:37 PM View Thread

Re: How to measure Output Wattage

2/22/1999 5:22 AM
Re: How to measure Output Wattage
Yer k-rect: The tone and volume controls, as usual, have a great effect, especially on a single frequency, 400 Hz input. I use a sine to check the output but watching the change in a square wave with changing tone controls is informative.  
The amp in question now develops 17.3W, max, inot a 7.5 ohm resistive dummy load but it's really dirty. The original tubes in this thang were 6973s which need a fairly hefty drive signal since I replaced them with 6BQ5s, due to availability from my junk box, I've got far too much input to the output tubes. Visibly clean waveform stops at 5.3w, crossover notch starts at 6.2w (need to replace the original 6973 cathode resistor), and the onset of clipping is around 10 watts.  
Actually the thang sounds pretty good with a little mid-range "hump" that I'll flatten out a bit. Fer the hell of it I'm going to eliminate the crossover distortion - this is where I really like a variable fixed bias supply. A turn of the old knob instead of the resistor sub box.