Muirhead Testing Set
Type D-30-A

s/n 314898

Muirhead Testing Set This is one of many instruments collected by Bob Evans which I have been given by his daughter Alice Kirby

It was very grubby when I received it and had several open circuit resistors and what appears to be a replacement centre zero 50 microamp meter(see the third picture below) I have cleaned the front panel and filled the engravings with off white emulsion paint which was allowed to dry before the surplus was rubbed off with a soft cloth. Apart from the missing top and carrying handle one of the original knobs had been lost, this has been replaced by a Cambridge Instrument type. The instrument came with a handbook which indicates that the serial number which has been scraped away was 314898. I believe this to be quite an early model possibly from 1930/1. The same instrument was produced for several years, one with serial number 352914 was sold on eBay for about 22

The ratio arms of the bridge are variable and controlled by the single switch below the meter which selects multiplying factors from .001 to 1000 (2000 ohms total). The rheostat arm consists of four decade switches totalling 11,110 ohms in steps of 1 ohm. An internal battery comprising two 1.5 volt cells can be used to power the bridge. terminals with links enable th instrument to be used with an external supply (including AC up to 10kHz) another galvanometer or indicating device  or standard resistor. The key operated switch on the left enables the test set to be used for cable fault detection. It is suited for Murray, Varley and Pomeroy's testing methods.

Alexander Muirhead
founded Messrs Muirhead and Company in 1894. He was a highly skilled electrical engineer, and his laboratory in Downe had an international reputation for the design and construction of telegraphic instruments of the very highest quality. Muirhead established the technological supremacy of the company in the fields of telegraphy and was the first man to make a recording of a human heartbeat. Muirhead and Co. went on to supply the first X-rays to Beckenham Hospital at the turn of the 20th century. The factory which was situated in Elmers End, Beckenham, Kent was demolished and replaced with a Tesco supermarket in the 1990's. Their research department and offices were moved to an office block which was built on the site of the Odeon Elmers End in the 1960s. When the firm closed down Maunsell (now part of Aecom), a firm of consulting engineers took it over and named it Maunsell House where I worked for a short time in the early 1990's. It is now converted to flats.

Want to more about the history of the firm? Have a look here