landman, the only Compass known for great depths, was the Challenger X-100 or X-200. Those were circa mid or late 1980s motion detectors, that would probably be similar, in depth, sound, characterisitics, etc... as the 6000 Di pro (IMHO). Great for their time, but no, I don't think they'd beat out some of today's power-house deep-seekers (like the Explorer for instance).
The 77b does not have a cult following for its depth. In fact, it is lousy on depth, has no ground balance, is a bear to keep smooth, etc... The value of the 77b was that it seemingly sees through iron. Ie.: it rejects nails and small iron, when the iron is solo. But put a coin underneath 3 or 4 nails, and you can usually still get a conductive hit. For that reason, it makes a good ghost town hunting machine, where zillions of nails abound. The deepseeking VLF (or multi-frequency, etc...) machines of today would mask under those circumstances. But the depth was limited to perhaps 4" in iron ridden environments. Perhaps 6" in clean turf hunting. So you can see, the depth is way behind today's machines, if depth were your only goal. And as for lack of ground balance on those old all-metal TRs, there were some states that (like parts of the rocky mountains, and vast stretches of mineralized beaches, etc...) that you couldn't even use the 77b on.
