Medresco Hearing aid
model OL35/A



Medresco Hearing aid OL35/A with earpiece. As issued by UK National Health Service (NHS) from 1955. These hearing aids were named after the Medical Research Council, which held an inquiry into hearing aid design and cost as the government made plans for the new health service in 1948. Development of early hearing aids for the NHS was provided by engineers at the GPO (the forerunner of British Telecom)

This is a three valve unit which needs a 1.25 volt filament supply and 15 volt HT, these would have been supplied by a 1.5volt cell and a 15 Volt battery contained in a similarly shaped battery box and carried around in a leather pouch. The HT consumption is about 250 microamps and the total filament consumption is 20 milliamps.  The output valve is a DL64 (CV2331) pentode with 1.25 V 10 mA filament and the two preceding ones are DF64 pentodes with 0.625 V 10 mA filaments wired in series. The valves are wire ended, the anode being that nearest the red spot the other electrodes in order are g2, f+, g1 and f-g3

It was given to me by Godfrey Manning who kindly also supplied the following pictures. He understood that it was found in a hospital audiology department long after being replaced by transistorised ones. A consultant doctor, who happened to be an electronics enthusiast, met the audiology technician carrying the box of aids down the corridor for disposal and he rescued them!


Two views of the interior


The connections to the batteries are by two plugs mounted on a multicore cable

The Post Office were contracted by the Medical Research Council to manage the contracts for hearing aids and in common with other equipment made for the Post Office would be marked with a manufacturers code ( The rear of this one is marked with the model number OL35/A and W/57 which indicates it was made by STC under a contract dated 1957. The earpiece marked with the model number OL375 and a date code E 8 /59 which would be the code for Ericsson (later Plessey).

Elsewhere on the internet I have found that STC Footscray (KB division) had the contract for producing Medresco hearing aids in 1957. Ian Dyer who has worked at Whiteley's since 1968 advised that they also made the Medresco hearing aids. This model was supeseded by a transistor model which only required a single 1.5 Volt cell. See one that I have here