Try a short version this time.
The idea was that gold rings,coins etc being heavier than ringpulls and foil would sink deeper.
Use an off shoot of the depth reading system introduced I think by Whites. No meter needed the detector had an extra circuit that worked out approximate target depth and just did not pass on the audio response from a target that was within a few inches of the coin. Compass and Tesoro both developed machines with depth blanking. The more sophisticated allowed the depth to be ignored/blanked to be adjusted so you could decide to take out down to two inches or more if required. The simple versions would just ignore say the top four inches with no adjustment allowed.
Drawbacks....worms,ploughing etc means rubbish can go deep and good stuff can be brought up to the surface.
The system ignored all metal both good and bad. So if blanking to four inches is used and a gold coin was at surface or any depth down to four then it would not give an audio response.
It would be picked up but you would not know.
Worse each bit of metal good or bad which you are not allowed to hear blocks the signal from deeper down and target masks out sideways.
As for old machines they normally were heavy, used more batteries and needed more skill to use to good effect.
On the other hand many turned out to have unexpected abilities like iron see through or the ability to find deep coins of unpure metal (ferrous contaminated) that modern machines would reject as being iron. Most non motion detectors had far less problem with steel washers,crown caps etc than modern motion machines.
Not having to move the coil to detect was a great advantage. No filters so no worry about keeping to the correct sweep speed. Hole in a rock or tree ? Just shove the coil in. No need to wriggle it about. And in high rubbish areas discriminating by just sitting the coil dead over the target knowing that a motion machine might well be picking up one or two other targets as its coil is swept giving you a false reading.
Problem with the old classics is that if you don't have a modern detector you will need two or three old machines to get you on different sites. What makes one work well on one site means it will be really poor on another.
Re cost I had a couple of machines twenty years ago that each cost more than an Explorer does today and money was money in those days. So not cheap.
