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Loctal tubes were originally conceived for car radios. Cars of the 30s and 40s rode pretty rough and tubes would occasionally work loose.
Loctals are also more reliable and cheaper to manufacture since the tube pin extends directly through the glass envelope. There is no additional plug threading and soldering operation. Later they were phased into other products as well. It also gave Philco and Sylvania a differentiated product since RCA was marketing metal tubes at the time.
Don
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