Sujet Régler le bias sur Acoustic 220

I've owned an Acoustic 220 for a while that generally sounded great, but I could always detect a little kazoo-like fuzziness that seemes to be the most audible when playing the D or G strings up around frets 10 thru 15 on the bass. I narrowed it down to the power amp board by using a separate pre-amp into the 220's power amp input.

I replaced all the electrolytic caps including the two large cans and changed out the 40408 and 6474/6476 driver transistors and the PN2484 bias transistor (Q6) that I thought might have gotten stressed over time. All circuit voltages checked out resonably close to what the Acoustic 220 schematic called for. After all this I think things might have improved marginally, but I could still hear some fuzziness.

Looking with a 'scope and the amp loaded to 2 ohms with 10mV of 1kHz drive applied I couldn't really see any crossover notch.

Next I wanted to verify that the idle current was between 25 and 30 Watts as specified, but I wasn't sure exactly where to measure. What I ended up doing was removing the drive signal, keeping the 2 ohm load (as indicated in the bias adjustment procedure on Page 2 of the Acoustic 320 manual), and placing an ammeter in series between the large power supply electrolytic's positive lead and the red wire feeding the power amp board. Does anyone know if this is the correct place to measure the idle current measurement? I calculated the idle Wattage drawn by the power amp board this way (supply voltage multiplied times amps) to only be about 5 Watts, way low.

The Acoustic 220 schematic says that the select R19 bias resistor should range from 560 ohm Min to 820 ohm Max, with 680 ohm being typical. My amp had a 560 ohm resistor for R19. I lifted one end of R19 and clipped a 1k ohm pot in its place. I started out with the pot adjusted to 560 ohms to match the fixed resistor it was replacing, but then to get up into the 25-30 Watt idle range I needed to adjust the pot down to around 470 ohms, less than the mimimum listed in the table on the schematic drawing.

I hooked the amp back up to a 406 cabinet and the fuzziness seems completely gone now, so I'm thrilled about that. I just don't want to overheat things or fry my output transistors if I'm wrong about the bias method. So does this all sound OK to any other techs out there?