Yup, the 77b was way ahead of its time, in the arena of all-metal TR's. So smooth, so deep (relative for its day), and so easy to use.
The fellow that got me into detecting, in the mid 1970s, was using a 77b. There was no discriminators at the time .... Well, there were a few we saw advertised in that very-early beginning. Discriminators had only just been out for just a year or two by the mid 1970s, so .... a lot of us were still running around with all-metal TRs. The rumor we'd heard is, "you might miss rings", doh!
Anyhow, the fellow that got me into it, around 1976 or so, had had this 77b for a few years already then. He told the funny story about how his older brothers had gotten this 77b for their youngest brother, to "keep him occupied" and let him "tag along" when they went to the school yards to detect. Meanwhile these older brothers each had their monster-sized Whites blue box machines, like the 66TR (which is 2x the size of a 77b!). And they just assumed the 77b was akin to a "toy", since it was smaller, lighter, etc... I guess back in those days, people just assumed that smaller must mean less sophisticated, less power, or whatever. Well imagine their surprise, when their young squirt 11 yr. old brother started spanking their coin finds and depth! They all went out and got these new-fangled Compass machines.
another compass 77b story: In 1980, our city tore out all the downtown sidewalks, to replace with new concrete walks. When the old concrete from this 1870's district was torn out, 6 or 7 of us md'rs were "all over it". And sure enough, seateds, barbers, etc... were found. But along comes this guy swinging a 77b. We looked down our nose at him, since .... obviously, "he had a dinasour", with no discrimination, etc.. And we figured our 6dbs, 6000s, VLF/TR's, etc... all go deeper, are newer, etc... Well imagine our surprise when his humble 77b spanked all these "new machines"! The 77b user tried to explain that it "didn't see the nails". At the time, that made no sense to me. I mean, ... my VLF/TR, and my friend's 6000's have the ability to pass nails too?? It wasn't till years later, that I began to understand the difference between "seeing through" and "discriminating out". This guy and his 77b could go through beds of nails, and pick out targets, while our TR disc, and VLF disc. was horribly masking. That's why, to this day, the 77b is still a good ghost townsy machine, in some situations.