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ID = 28989
United States of America (USA)
Brand: Moorhead Laboratories (Pacific); San Francisco
Tube type:  TRIODE (Detail uncertain)   Detector 
  <1925 very rare. ***
Identical to A-P_Solenoid
First year 1923 ?? Saga of the Vacuum Tube, Tyne page 179, 180

Base UV-Base (4 Pins+Bayonet, USA 1914 WE)
Was used by Radio/TV-reception etc.
Filament Direct / Battery =

This tube was designed by Henry K Huppert. He was an x-ray technician and later was employed by Moorhead Laboratories, where he worked on this tube and the 2 in 1 tube. He applied for a patent on the solenoid tube on 19th January 1923. Patent no 1564070 was granted to him on December 1st, 1925. No record exists that he assigned his invention to Moorhead Laboratories, but retained ownership of it. Many experimental tubes were made before a commercially successful tube made and several of these were submitted to Moorhead for approval. At least one tube had a copper coil control. The coil was a control element with the wire coil outside the plate.

History of the tube is covered extensively in the article "Henry K Huppert and his tubes" etc, by Eric P Wenaas, which is in the Antique Wireless Association's Review, volume 30, 2917, pages 173-222.

Information source Saga of the Vacuum Tube, Tyne   page 179, 180
-- Collector info (Sammler)   
  A-P_Solenoid: Fin Stewart
Fin Stewart
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A-P_Solenoid: Fin Stewart collection
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