Very interesting zenith observation

[andy]

I know mine has an efficiency coil because I remember adjusting it when I first got the set going. There was at least one revision to this chassis. The later revision had a flyback that was potted in silicone and there was a varistor in the the HV regulator circuit. The early one uses a different potting material and has a silicon diode in the regulator near the HV control. I can't remember if it eliminated the need for the efficiency coil, but it may have if the flyback was able to handle higher temps.