Hi again Monoperm Supers used to sell at around the £50 mark but a realistic price with the box is about £20. They are 5 pole motors and must have cost a fair bit to manufacture. Although it says 6 volts on the motor they will run from 7.2 volt pack as long as not heavily loaded. A nice quality brass 35 mm prop is about right as a load.
The last one I fitted was into a Billings Mary Ann and she goes well at half power but can stop dead to avoid a collision when in reverse.
In power it sits between a 385 and a 380 for power, more towards the lower end, these Mabuchi motors are much cheaper as they are produced by the million. So the monoperm and the Supers are for the discerning collector!
You may know that these Marx motors are part of a series of similar design motors. Going upwards there is a rather rare Duoperm then the more common Decaperms and the top one is a Hectoperm. Each of these can come with a 2.75 reduction gearbox.
But there were a lot of smaller Milliperms and Microperms made but only in orange and black and were much used in quality pre-proportional RC servos, which were really electric actuators.
The german RC producers used these where as in the UK they used the over engineered Victory Industries Mighty Midget electric motor. I have a Mighty Midget in an original Hobbies Anglian trawler and she still goes nicely under power.
The Marx motors started in an orange and black form and stayed that way for many years and then were re-worked into the silver grey now. I built a 1950s launch kit as a commission about 6 years ago and fitted a contemprory orange and black Hectoperm, as I have never seen another one before or since, I suspect it must be a collectors item now.
There were also bolt on epicyclic gear boxes for the mid-range of the motor types and then a pile gearbox where you chose the number of reduction sets you wanted.
The Hectoperm when last on sale had a retail price of £150.00 and by then had really priced itself off the market but they still fetch about £50.00 and go nicely with Meccano models.
For me, I like them and they tend to be my first choice.
kind regards
Roy