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Mullard PM4 box

PM4 exhibit
    
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This box has a date label of 1928 inside it but this style of box construction is more typical of the early to mid 1920's. The box is constructed as printed paper over millboard. The inner section is plain cardboard lined with horsehair. The box lid is missing its square of horsehair wadding as the top cushion. The cardboard box is 82 mm square and 141 mm long.
Guarantee: This valve is guaranteed for a period of seven months from date. In case of this valve failing during this period the valve should be returned to us together with fourpence postage and packing and sixpence for each month the valve has been used. A new valve will be sent in exchange BY RETURN OF POST.
This valve is rated at its best working consumption and the voltage should be so adjusted as to give the best results with a minimium amperage. The average LIFE under these conditions is 1,000 hours, after which the efficiency falls off considerably. Any HT up to 200 Volts can be safely used.
Our aim is to give good and prompt service under any conditions. PR Valves 17 Paternoster Squate EC4. The date is 13 Nov 1928.

 

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