38V AC on AMEK PSU Output rail
After turning my AMEK 2000 PSU on and checking for the proper dc voltages on outputs ( +18, 18 and +11 ), I swapped the multimeter scale to measure AC voltage and...holy ****!!! Look what I got...
+18 rail= 38V AC  18 rail= 0,0V AC +11 rail= 24,8V AC It sure does not look right, even for my electronics untrained self!! 
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J.P. Ambrogi BRAZIL 
Sounds to me like you are not measuring correctly, maybe to the wrong ground.

The multimeter has a rectifier to measure AC, in this case probably a half wave one, and then calculates RMS voltage from integrating the rectified voltage and multiplying by 2 (for a half wave rectified sine wave, Vrms = Vpk / 2 *) plus some correction for voltage drops on the diodes. The numbers and the fact that the negative supply measures 0 make perfect sense. Just to check swap the probes and you should get 0, 38 and 0.
* Edit: to be precise, it should multiply by PI/SQRT(2) ~ 2.22, since for a sine Vrms = Vpk / SQRT(2) and for a half rectified sine Vaverage = Vpk / PI. 
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You need to understand which wires connect where. The chassis of the power supply should be connected to mains ground. The supply outputs may not be connected directly to ground, so the supply floats. Then the frame of the mixer should be grounded to mains ground, and the supply may bond to ground there.
So you have to identify exactly where to measure. Modern meters have high input impedance, and will read stray voltages easily. 
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