While most tube collectors are familiar with the DeForest DV-DL series of tubes, the DV-9 is one member of the family unknown to most and seen by very few. The main reasons for its obscurity are the almost complete lack of advertising and the fact that it was replaced by another DeForest tube less than a year after its introduction. The only known ad for the DV-9 was in an announcement in QST magazine for July of 1926. This ad gave little information, simply stating that the DV-9 was a low power transmitting tube for short waves. The price was given as $9.00. There is no picture, only a fairly crude line drawing which shows the spherical bulb but does not show the tip. Also listed in this same ad was the DV-9R rectifier, a tube even more obscure than the DV-9. There is no drawing, only a description which states that the DV-9R is similar in design to the DeForest HR rectifier, only intended for lower power. Recently a tube was seen that appears to be a DV-9R. This tube closly resembles the DV-9 with the grid omitted, and like the DV-9 has no marking.
As shown in Fig. 1, the DV-9 has a spherical bulb about 2 1/4 inches in diameter, and an overall height of just over 4 inches. There is no marking on the tube, other than the standard info on the base. There may have been a paper label at one time, however the few other known examples of tubes that fit the DV-9 description were also without marking. The other examples were also heavily gettered such that the internal structure could not be observed. Fig. 2 shows a close-up of the internal construction. The large box plate and center spring loaded filament support give this tube the look of a scaled down Singer power tube.
The ad gave no operating data of any kind, but by various empirical methods it was determined that the filament voltage was 7.5 volts, at which condition the filament drew 1 amp. The input power is estimated to be about 15 watts. Note that this tube is not an early version of the DL-9. The DL-9 was strictly an audio amplifier with a different design and not interchangeable. In 1927 the more familiar type D transmitting tube was released and apparently replaced the DV-9. The D had a larger pear shaped bulb and a filament that drew 2 amps at 7.5 volts. A companion rectifier to the D, the DR, was most likely the replacement for the DV-9R.