D_Moorhead-E12

This tube is a single ended type with an E12 screw base and was first made in the middle of 1921 . The anode and grid connections are wire leads that come from opposite sides of the (insulated) skirted part of the base. The diameter of this skirt is 27 mm. The tube was made in limited quantities and appears to have been based on the earlier de Forest CF185 as it is somewhat similar in appearance and electrically the same. It could be operated with 30 volts on the anode. Versions of the tube have been seen with a UV base and this was a later tube - around 1923 - used as a replacement for tubes with the obsolete E12 base. The tube is not to be confused with the Moorhead D (ER_1917). The tube is mentioned in Tyne's "Saga of theVacuum Tube", page 179 and the illustration shows the tube with a paper label which reads: "Moorhead Tube Electron Relay Series "D" Plate 5 to 50 volts Filament 6 volts Current not to exceed .84 amp. It is interesting to note that the tube in the color photo has the base skirting tapering slightly narrower at ther bottom whereas the tube illustrated in Tyne has the skirt with parallel sides.