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so in the process of tracking down the oscillation problem in my pse 6l6 amp, i disconnected the bypass cap and the motor boating ceased. i've tried different values, from 75uF to 1000uF but none of them seem to help very much. i aslo modified the power supply a little bit. now it feeds into a 10H choke, 27uF cap, 56ohm series resistor, and a 330uF cap. everything else feeds off this point with various resistors and caps. increasing the cathode resistance seems to help also, am i just in at a bad operating point?
If none, add one. If yes, replace it with a double value.
Your question is failing to provide information sufficient to even hazard a guess. But hell, I'll play. Let me guess. Your cathode resistor is between 220ohms and 330ohms, isn't it? If it is then I would guess that the tune of your power supply is being picked up and amplified by the tune of your cathode resistor and cathode by-pass capacitor. Try a series of by-pass caps starting with 10uf, 20uf & so on until the motorboating starts up again. Then use a smaller by-pass cap.
What kind of amp are talking about? Push pull or single ended? Im assuming if it has a 330 cathode res its SE.When you say bypass cap do you mean in power supply or cathode of output or driver? This would help a bit.
Any feed-back curcuit?
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