Mullard valve TDD4. The gold spray coating served no purpose other than to hide the blackened interior as Mullard valves were still manufactured using the azide process, long abandoned by other makers.[1]
Famous Mullard EL34 Power Pentode
Current Russian production Mullard EL84 valve.

Mullard Limited was a British manufacturer of electronic components. The Mullard Radio Valve Co. Ltd. of Southfields, London, was founded in 1920 by Captain Stanley R. Mullard, who had previously designed valves for the Admiralty before becoming managing director of the Z Electric Lamp Co. The company soon moved to Hammersmith, London and then in 1923 to Balham, London. The head office in later years was Mullard House at 1–19 Torrington Place, Bloomsbury, now part of University College London.

Partnership with Philips

In 1923, to meet the technical demands of the newly formed BBC, Mullard formed a partnership with the Dutch manufacturer Philips. The valves (vacuum tubes) produced in this period were named with the prefix PM, for Philips-Mullard, beginning with the PM3 and PM4 in 1926. Mullard finally sold all its shares to Philips in 1927. In 1928 the company introduced the first pentode valve to the British market.

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