All required service performed in accordance with manufacturer with ORIGINAL components, NO cheap substitutes or re-stamps are ever used. Every switch and potentiometer, if equipped, is washed with Caig Deoxit, then rinsed a second time.
Amplifier section DC offset, if adjustable, is set to exactly 0mV, and allowed to idle for 45 minutes to confirm stability. Afterwards, the amplifier section is CORRECTLY biased to eliminate all crossover notch at the transition between device polarities (push half of signal switching to pull half of signal). This is done into a 4 ohm load at 10kHz with one watt of output. This impedance resolves, visually on the oscilloscope, any crossover notch, regardless of the impedance connected in normal use. The frequency of 10kHz is also used being as harshness from under biased output stages almost always manifests in the 10th octave of human hearing 10kHz~20kHz. It is set to the point where the output is free of crossover notch, and locked in.
Just enough forward bias for a clean output, and a cool running output stage. This all applies to direct coupled output stages. In older capacitor coupling output designs, the AC balance of the output stage is set using the permanent user impedance (usually 8 ohms) for symmetrical full power clipping, performed at 400Hz and again at 1kHz, which is extremely important. This allows both halves of the signal to clip at the same point during full power transients. Bias is set in a traditional fashion as outlined above for direct coupled output stages. After confirmation of all functions and designed output power, the unit receives a complete external cleaning and detail removing all foreign substances.