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Old 3rd April 2007, 06:37 AM   #1
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Join Date: Mar 2005
Location: Aussie
Default Need help ahve "dog leg" shaped waveform on my amp

Can anyone help with a good procedure for tuning my guitar amp?

The amp runs 4 x EL34 tubes in push pull and each are running 33mA each tube at the moment but on the oscilloscope there is a "dog leg" shaped sine wave thru the zero crossing (8 OHM load).
Should I increase the bias current on each tube in turn? (There are adjustments pots for each tube)
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Old 3rd April 2007, 08:23 AM   #2
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Join Date: Jan 2004
Location: Jakarta
Looks like it. This is likely to be crossover distortion, caused by one tube ceasing to conduct before the other has started conducting fully, a common problem with Class B or very lean Class AB. Try increasing the current in small increments, to find the point where the kink disappears. (If it doesn't disappear, then the problem is something else!)
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