[MrFixr55]

A 12H 650 and a TO? Which one? I'm envious. You have a great eye, lucky as heck or you have some money and an understanding spouse, all of which I lack. I do have an 8Goo5, first of the post war TOs. Seems that the newer ones are more desirable, but it seems that 1L6 convertor tubes used in the newer models are getting pricy. Mine does use relatively common 1LC6 or 1LA6 convertor and IMHO has a closer relationship to the Clipper / Bomber pre-WWII version.

The only reason that they have put a cap before the resistor on Line D is because the AVC Diode does not serve as the detector. Yes, the resistor before the cap does cause a time constant, but since Physics II in college was 50 years ago, don't ask me to calculate. It is also interesting that there seems to be a rather fixed bias there also, from R61. Note that the center tap of the HV supply is not B- in these sets, chassis ground is. Since the HV PS center tap is more negative (by about 65V, thanks to R61, this is almost akin to C-, and since this is tied to AVC line D through 470KOhm and to Line C through 1.47Megohm. there is a pretty good negative bias on these stages already. I have not seen AVC like this before.