Spare 812A Electron Vacuum tube sold ONLY with purchase of M.O.P.A. amplifier:

We require that our international customers purchase a spare vacuum tube (812A) at the time of their M.O.P.A. amplifier order. One 812A vacuum tube is included with the M.O.P.A. amplifier, however, it's a good idea to have a spare on hand if you're involved with a research protocol and cannot afford a day off (or longer) if something were to happen to your tube. Usually the tube will last for years, but there are occasions when human error can inadvertently break a tube and another one is needed right away. If you need to order a tube at a later date, the cost of shipping an extra single vacuum tube by itself to an international destination is relatively high with expedited FedEx or USPS courier services. It can also take up to a week or longer to receive. Our experience with this technology is that it is wise to have a spare vacuum tube on hand at all times. The extra 812A tube will be shipped inside your M.O.P.A. amplifier in packing material. To add the spare vacuum tube to your order, click on the "Add to Cart" button. The cost is only $43 when purchased with a new M.O.P.A. amplifier.


SKU: 812A
  • NOTE: The 812A vacuum tube is not sold separately to the general public from our company. It is ONLY sold and shipped at the time of purchase with a new M.O.P.A. amplifier. Please call us if you need to order a fully tested 812A vacuum tube and we will put you in touch with a supplier. 

  • Back in 1904, British scientist John Ambrose Fleming first showed his device to convert an alternating current signal into direct current. The "Fleming diode" was based on an effect that Thomas Edison had first discovered in 1880, and had not put to useful work at the time. This diode essentially consisted of an incandescent light bulb with an extra electrode inside. When the bulb's filament is heated white-hot, electrons are boiled off its surface and into the vacuum inside the bulb. If the extra electrode (also called an "plate" or "anode") is made more positive than the hot filament, a direct current flows through the vacuum. And since the extra electrode is cold and the filament is hot, this current can only flow from the filament to the electrode, not the other way. So, AC signals can be converted into DC. Fleming's diode was first used as a sensitive detector of the weak signals produced by the new wireless telegraph. Later (and to this day), the diode vacuum tube was used to convert AC into DC in power supplies for electronic equipment.

    Many other inventors tried to improve the Fleming diode, most without success. The only one who succeeded was New York inventor Lee de Forest. In 1907 he patented a bulb with the same contents as the Fleming diode, except for an added electrode. This "grid" was a bent wire between the plate and filament. de Forest discovered that if he applied the signal from the wireless-telegraph antenna to the grid instead of the filament, he could obtain a much more sensitive detector of the signal. In fact, the grid was changing ("modulating") the current flowing from the filament to the plate. This device, the Audion, was the first successful electronic amplifier. It was the genesis of today's huge electronics industry.

    Between 1907 and the 1960s, a staggering array of different vacuum tube families was developed, most derived from de Forest's invention. With a very few exceptions, most of the vacuum tube types in use today were developed in the 1950s or 1960s. One obvious exception is the 300B triode, which was first introduced by Western Electric in 1935. Penta's PL300B version of the 812A, plus many other brands, continue to be very popular with audiophiles around the world. Various vacuum tubes were developed for radio, television, RF power, radar, computers, and specialized applications. The vast majority of these vacuum tubes have been replaced by semiconductors, leaving only a few types in regular manufacture and use. Before we discuss these remaining applications, let's talk about the structure of modern vacuum tubes. SEE ARTICLE... Click Here.

DISCLAIMER: We do not call our instruments Rife Machines or a Rife Machine like many other companies do. Dr. Rife specifically stated that he "did not want his name put on any machine" because "some people" might use his name to sell their frequency machines. Those companies who respect his wishes do not call their machine a "Rife Machine." The function generator and amplifiers on this website are sold as electronic test equipmentInformation disseminated on this website is public knowledge for educational and research purposes only. It should not be construed as any type of medical advice and you accept responsibility for any actions you may take. No suitability, claims or merchantability for any recommended purpose or use is stated or implied. This website is available to help you research and learn more about frequency generating machines. The manufacturer of this equipment is in no way responsible for the information supplied, or use of the products, for anything beyond your personal research. No statements on this website have been evaluated by the Food and Drug Administration.

Any product mentioned or described on this website is not intended to diagnose, treat, cure, or prevent any disease.

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