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ID = 70216
Brand: Philips; Eindhoven (tubes international!); Miniwatt
Developer: Valvo GmbH, Radioröhrenfabrik; Hamburg 
Tube type:  SPECIAL TUBE, other or unknown 
Identical to XL7900

Base Magnoval (9-Pins), B9D Top contact with a cap.
Was used by Technology / Measurement

This is a very special vacuum-sealed vibrating capacitor, intended to operate as modulator for very feeble DC signals, replacing electro-mechanic vibrating choppers. Amplifiers capable of measuring currents as low as 500 electrons per second have been realised using this device.

  • Insulation resistance greater than 1000 teraohms
  • Capacitance of Cdr and Cm 35 pF
  • Resonating frequency between 5.3 and 6.3 kHz.

Magnoval base, gold-plated pins

* Cdr = Driving capacitor

* Cm = Measuring capacitor

Philips Holland design.

Information source -- Original-techn. papers.   
XL7900: H.F.
Herbert Flick

More ...
XL7900: Manufacturer's Literature
Emilio Ciardiello


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