Hey digger27, I believe the first generation "Judge" was simply a 77b, with the addition of a TR disc. added. So that would have been a TR/TR machine (versus a VLF/TR machine). The first "TR" indicated the all-metal mode (which was like the 77b), and the 2nd TR is what became familiar on a whole host of mid-to-late 1970s machines.
Their days were numbered though, since starting in about 1978, vlf-disc (aka motion disc, or geb disc) took the world by storm!
I have a 77b I take out for certain iron/nail riddled locations. Circa 1971 to 74-ish. Like ghost-townsy sites. They could see through up to about 4 nails at a time, while still seeing the conductive target underneath. Thus good for spots that give modern power-house discriminators fits with masking.
However, the benefits ended there. In all other ways they were a dinasour. No other form of disc, a bear to keep balanced, poor depth (compared to later VLF's), poor in minerals, etc.... Max depth on a coin was perhaps 4". Maybe 5 or 6" if you had exceptional soil and balancing.