Modern vacuum tube collectors have been trying to find concrete evidence that the DeForest Type 20 was not only made but designated type 20. This author believes he has found what has been missing or perhaps re-found again within my information?

As all collectors know, Otis Moorhead was the first to bring together DeForest and, Marconi and create a working agreement to break the deadlock of the patent situation following WW1 that essentially meant that no maker could legally make and sell triode vacuum tubes. DeForest saw an opportunity to market a few of his own tubes as well and abide by the terms of the DeForest, Marconi, and Moorhead agreements. This arrangement was embraced by at least Moorhead as DeForest tubes were quite popular with the US military and amateurs alike and provided an outlet for more sales by the Pacific Radio Supplies Company.

Click on the ad and tube pictures below for a large version

The first DeForest made tube to be offered of this new partnership was the Type 20. Of course, the new DeForest tube had to have been made many months before but the first, and possibly only advertisement, in fig. 1, appeared in the Electrical Experimentor in May, 1920. While no picture is included in the ad, it is identifying the offering as the type 20 several times. RCA cancelled its contract with Moorhead, DeForest, and Marconi contract in July, 1920 so it could be presumed that DeForest never had a chance to sell his stock of type 20 tubes, or very few. These type 20 tubes can be ID’ed by having a shiny nickel base with only the words “Patent Applied For” stamped on the base and “DeForest” etched in a circle on the top of the glass bulb.

Fast forward to 1922 when Fleming allowed his patent to expire which allowed DeForest a chance to sell his type 20 tubes in 1923 and rename them the DV 6. So the first group of DV-6’s were his un-sold type 20’s. When the type 20’s were sold out as DV-6’s, he dropped the words “pat.appl. for” along with the etched word “DeForest”. Patent numbers were added along with the words “Sold Only for Amateur and Experimental Use”. Two distinctly different versions.

Please see the tube pictures below along with a description of each.

Fig. 2. The DeForest type 20 tube first offered for sale in May, 1920, 3 years before the DV-6. Again, my opinion, the DeForest type 20’s he did not sell in 1920 became the first group of DV-6’s he sold in 1923.

Fig. 3. Shown in fig. 3 is the DV-6 and it’s shipping box along with fig. 4 with a better view of the newly added words “Sold Only for Amateur and Experimental Use”. Both the early type 20 and the latter DV-6 were soft tubes.

Fig. 5. DeForest added the DV-6A and advertised it in Sept., 1923. This was the hard version.

Figs. 6 & 7. 6 is the early short version of the VT 21 that came from the Edwin Armstrong collection via Tyne. Fig. 7 is the later taller version of the VT 21.

Click on document below to enlarge

The January, 1947 issue of Radiocraft magazine featured a tribute to Lee DeForest. Within those pages, George Clark, (1880-1950) famous collector, played a personal tribute to DeForest. Fig. 8

An unknown picture taken by Gerlad Tyne is one that Clark choose to include.

As can be seen in that picture are two, what Clark calls, type 20 tubes along with one version of the WW1 DeForest VT 21 on the left.

I think Clark mis-identified the tube on the far right as a type 20 when clearly, it’s a DV-6A. Never-the -less, I am in no position to second guess Clark calling the tube in the middle a DeForest type 20, which it is.

Here is the entire magazine article in fig 7 as it relates to DeForest here: RAD