"Compton Don" calls. He asks me to double check, and, indeed, I find I had stupidly turned on the "Compton PhotonDetector Spare", not the "Compton Photon Detector".
Aargh.
Mea Culpa, Mea Maxima Culpa
I turn on the Photon Detector HV to 1700 V, see a reasonable anode current, and see actual rate from the detector.
Stop present Compton run, and start new one: Run 22986.
Signal/noise looks like about 5:1 in photon detector.
Thanks, Don, for calling in...