Wojtek,
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I suggest verifying that adjusting the PABias1 pot does change the voltage on the MOSFETs' gates.? As Gordon stated, you need to be careful when making this adjustment.? It is very easy to drive the MOSFETs to destruction, and the current will "jump" as you get close to the nominal setpoint.
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A safe way to test the bias control is to measure the resistance from the MOSFETs' gates to ground without power connected.? You should be able to vary from almost zero ohms (55 ohms) in the fully counterclockwise direction to nearly 10k ohms when fully clockwise.? Be sure to return the control to the fully counterclockwise position before restoring power.
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In addition to a faulty control, one of the bypass capacitors may be shorted.
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73
Evan
AC9TU
