"The Road to The Transistor". Copper Oxide Rectifiers should behave as a Varactor in the MegHz range.
http://www.jmargolin.com/history/trans.htm "The copper oxide rectifier was invented in 1927 by L.O. Grondahl and P.H. Geiger. Copper oxide rectifiers featured good conduction of forward current but poor reverse voltage rating, about 6 Volts. However, because they could be built on plates instead of with a point-contact, the larger surface area meant they could handle large currents (about 7 Amps) and were used for awhile in battery chargers. U.S. Patent 1,640,335 was issued August 23, 1927 to Grondahl. For some reason Geiger's name is not on the patent. (Thanks to Reader Dave for finding the patent and noting that Geiger's name is not on it.) That's a good question, why isn't Geiger's name on the patent since the reference for Geiger is: L.O. Grondahl, P.H. Geiger, "A New Electronic Rectifier", Proc. AIEE Winter Convention, p.357, NY 1927. [The American Institute for Electrical Engineers (AIEE) merged with the Institute of Radio Engineers (IRE) in 1963 to form the Institute of Electrical and Electronic Engineers (IEE! E).] The patent is assigned to the Union Switch & Signal Company. George Westinghouse founded Union Switch & Signal in 1881, consolidating the assets of companies that had pioneered closed track circuits and interlockings. It operated as an independent company until 1917 when it became a subsidiary of Westinghouse Air Brake. It's still around as a wholly-owned subsidiary of Ansaldo Signal. http://www.switch.com/uss_history.html. The largest and longest use of copper oxide rectifiers was in multimeters so that a DC meter could be used to read AC voltages and currents. Simpson Electric Co. still uses copper oxide rectifiers in their non-electronic multimeters. [1] The ones they use have a small surface area to minimize the capacitance which results in a rectifier with high bandwidth extending to the video range." " On January 28, 1930, U.S. Patent 1,745,175 was issued to J.E. Lilienfeld for a "Method and Apparatus For Controlling Electric Currents." The patent shows an insulating material, such as glass, coated with a metal film having "unidirectional conductivity." There is no evidence that the device actually worked but it was a brilliant hunch. The material to actually build a transistor just didn't exist at that point. In 1939 William Shockley and Walter Brattain made an unsuccessful attempt to build a semiconductor amplifier by inserting a tiny controlling grid into a layer of copper oxide. The Second World War put an end to their experiments." I think Dr. Moray's Coherer and other before-it's-time solid-state amplifier circuitry can be replaced with a husky Varactor Diode. The Antenna, Ground, and Load are still required. http://tpub.com/neets/book11/45k.htm "An increase in the charge Q or a decrease in the capacitance C causes an increase in the voltage across the plates. Thus, a voltage increase, or amplification, can be obtained by mechanically or electronically varying the amount of capacitance in the circuit. In practice a voltage-variable capacitance, such as a varactor, is used. The energy required to vary the capacitance is obtained from an electrical source called a PUMP." Fred
