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LOEWE 3NF VALVE, 1929
3 x triodes, Cathode 4V- anode 90V.
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One of the most fascinating valves you will ever see, the Loewe 3NF incorporates three triodes, two capacitors and four resistors in a single glass envelope. The inclusion of the passive components reduced the number of pins required to six, but to avoid them contaminating the vacuum, they are each sealed inside a glass tube.
One of the reasons for the development of this amazing device was that in Germany, there was a tax on receivers based on the number of valves in the set, so in 1926, Loewe Radio A.G introduced the 3NF, and also another multi-valve, the 2HF, which contained two screen-grid tetrodes, two resistors and a capacitor, intended for use as a two-stage RF amplifier.
The original Loewe multi-valves are masterpieces of glass work, which must have been very expensive to manufacture, so later versions used a mica supports, and the glass was given an aluminium outer coating to hide the less elegant internal structure.
An obvious drawback of putting three valves in a single envelope is that if one filament fails, the whole device becomes useless, but to counter this disadvantage, Loewe offered a repair service to replace failed filaments.