Does the hum remain if just the Quickie is plugged into the power amp, but no sources are connected?
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Apologies for not responding earlier to the help provided. Work! Anyway, I just unplugged the CD components, powered on the Quickie and powered on the amps. The loud hum is gone.
Now to step 2 - amps off, Quickie off. Unplug digital cable from output 2 on the 47 Labs transport. Reinsert in output 1. Plug DAC into Quickie. Put Quickie on different level from CD rig. Turn on Q and amps.
Sonic mayhem, loud ringing! Put finger on DL92 tube. Ringing gone, I presume I have gotten my first lesson in the legendary microphonics of the DL92 (Mullards I bought for the project). Press play on CD.
SUCCESS!
Time to listen to this thing!