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The EM1 Tuning Indicator

G O Thacker, BSc and R Y Walker, ARIC, Wireless World, January, 1947.
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The 'genuine' EM1 and the war-EM1 on the right.

During the course of constructing apparatus incorporating a 'magic eye' tuning indicator we discovered that there are in existence two distinct types of Mullard EM1 tuning indicators that can give widely different results. Our first EM1 (hereafter referred to as the War-EM1 had a domed top, no transverse cathode screen support wire, and round deflector rods giving a two-part field. The second EM1 (the genuine article) had a recessed top, transverse cathode screen support wire, and flat deflector vanes giving a four-part or Maltese cross field.

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