mystery security metal detector

[paul47]

Hi can anyone help? I purchase a security metal detector at a car boot
the label says METAL DETECTOR Mk. 4
AVIMO LTD
TAUNTON ENG.
Serial no. C240/77 AVL
The only controls are 1. on/off & 2. sensitivity a slide switch with high/low.
Low sensitivity will not pick up a 10p coin, high sensitivity will pick up a 10p coin at 3 inches. As soon as it is switched on it emits a continuous low tone which goes high pitched when a target is detected. It is only 19" long with a 4 inch dia coil . I can see a use when searching in confined spaces like buildings, caves, between large rocks etc. However i do have one query even though I have it working. ORIGINALLY IT WAS FITTED WITH A PP9 BATTERY CLIP ! but it was impossible to get a PP9 battery in the case WHICH LOOKS LIKE A SQUARE SECTION DOWNPIPE. I removed this & fitted a PP3 battery clip which now gives me the option of using 1PP3 or 6 x AA i.e. 9 volts. One other option is 8 x AA 12 volts. My main question is does anyone know what voltage this operates on or has anyone got a circuit diagram of this early detector. UNABLE TO ADD PHOTO TO ASSIST IDENTIFICATION

[ray77]

Can`t find anything about the detector but this is the origanal company http://www.gracesguide.co.uk/Avimo and this is the present parent company http://www.thalesgroup.com/property/
If you get in touch with them they may be able to help.

Ray