John Fleming, working for the Marconi Wireless Telegraph Co. in London and was the first to experiment with the Edison Effect light bulb. Some of the 2nd generation Fleming valves were tubular and were mounted in what became known as the “Gallows Type”. Third and fourth generation Fleming valves took on the shape of English light bulbs of the day. All were 2 part diodes, filament and plate only. The diodes above were made in the commercial form around 1919. The Fleming valve in the picture on the left is real but this author made the gallows frame.

Roy Weagant Worked for the American Marconi Company and tried to circumvent the DeForest Grid patent in any way possible. The experimental diodes above were two such attempts and as can be seen, an external grid was not added to the earlier valve on the left above. The external grid was added to the one on the right. I suspect that the black grease pensil number 2537 was added by Tyne but I am not certain.

With the Fleming diode patent to expire in mid 1923, companies like Electrad jumped into the market. All diodes of the time were generally used as a replacement for crystal detectors. Notice Electrad made a soft version as well as the hard version.

Modell’s mail order house presumedly made the Margo detector, again to replace the crystal in any crystal set. Modell’s claimed to have 9 locations in New York City with 191 Fulton Street being just one. Oddly, the Margo Detector tube has Fleming Valve inked on the base but had nothing to do with Fleming.

Delta Midget Tube Company made this diode with a brass external grid to circumvent the DeForest grid patent and Fleming diode patent so they must have released it before the Fleming patent expired in 1923 or thought the grid on the outside of the bulb would help, which it could not. What cannot be seen is the filament which is quite long and has a zig zag shape. It would have the same hook up as the Margo above.

Modell’s also sold the Dietzen Diode tube along with other Dietzen products. Notice that the Modell’s address in the ad above is 71 Cortlandt St., New York. This entire area was torn down to make way for the new World Trade Center. The Dollar tube shown above could have been sold by Modell’s or under the brand name Welch, shown below, or both?

The Welch Peanut Tube made by the Radio Research Guild; Newark New Jersey was another company making diodes. They were pinched down around the middle of the glass bulb and wrapped with a wire to be used as a grid. No help but it looked good.