These models were all powered by three 9V batteries. They were mounted in an 'under-slung' position below the rod and ahead of the hand-grip, or they could be mounted under the upper rod just ahead of the armcup.
The Coinmaster Classic I was hard wired with an 8" coil. It was a motion-only design.
The Coinmaster Classic II was also hardwired with an 8" coil. It was also a motion-only operation detector.
The Coinmaster Classic III had the Sensitivity and Discriminate controls like the Classic II, and it also had an interchangeable 8" search coil. It was able to use the early-style 4", 10" and 15" coils. In addition, it featured a Frequency Shift, Normal/Black Sand selector, and an All Metal mode for pinpointing.
About 1994 we saw the introduction of the Classic III Plus. This model had the same appearance of the other Coinmaster Classic's, but it had different circuitry. It came standard with the Blue Max 950 coil and it was compatible with all of the newer Blue Max series of coils.
I believe it was 1996 that we welcomed the introduction of the 'SL' (Slim Line) series of Classic's which used the same housing as the XLT with the 8-AA drop-in battery tray.
The new version of the Classic I and Classic II were very similar to the 'Coinmaster' Classic versions in that they still used essentially the same circuitry and the Classic I's 8" coil was hard-wired. The Classic II had an interchangeable 8" coil, but it was the Blue Max 256 that was able to be used on it and NOT the standard Blue Max series of coils.
The "Plus" name was dropped from the Classic III SL version, and the Classic III SL just used the same Classic III Plus type circuitry and all of the Blue Max series of coils. It still came standard with the 950 coil.
The 'original' Coinmaster Classic II and Classic III had very similar in-the-field performance as the newer 'SL' version of the Classic II. They were mainly hampered by poor search coil versatility.
The Classic III Plus had the same in-the-field performance as the newer version 'SL' Classic III. Very versatile with their wide-range of search coils available. These models were quick-response and fast recovery, slow-motion, silent-search designs with impressive depth of detection.
The Classic III Plus, and especially the latter version of the Classic III in the better balanced 'SL' package, have provided me with some of my best recoveries in over forty years of detecting, as well as some of the highest quantities of coins found in a given period of time.
Any specific questions? Shoot me an E-mail if you'd like to: MonteVB@comcast.net
Monte