As Jonathan Scull noted, with its 12 EL34 output tubes, the Cary CAD-280SA V12 sure do run hot. I let it warm up (literally) for an hour after installing the tubes, then adjusted the output-stage bias for each channel via the convenient rear-panel phone jacks. The trimpots' action is rather coarse—even an imperceptible twist with a screwdriver changed the bias current by tens of milliamps. The closest I could get to the recommended 275mA was 278mA in the right channel, 283mA in the left.
The Cary amplifier didn't invert absolute polarity. The signal/noise…