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![](/images/853.jpg) | .Abbreviated History Timeline of Early Radio Tubes in the USA | Fleming Valve. Although the chronology of radio tubes in the US really goes back to Thomas Edison and the “Edison Effect” (The minute flow of electrons from the positive side of the filament to a plate, a piece of metal inside a light bulb) Ambrose Fleming in the UK actually created the first radio tube. In 1904 if not before, Fleming found that his tube or valve, worked well enough to receive signals. The Fleming Valve was the first radio diode or two element tube; it could detect signals but could not amplify.
Audion. 1906-07. Lee Deforest added a few turns of very fine wire around the filament located between the filament and the plate. This new element was named the grid, and Deforest had produced the first three element tube, or triode. Deforest’s Audion would not only serve as a detector of radio signals but also could amplify them. The Spherical Audion was first developed in 1906-7 and was followed several years later by the Tubular Audiotron.
Western Electric. Western Electric in about 1915 began to improve on the audion and released a whole series of amplifiying tubes such as the VT1, VT2, 101D, 102D, 104D, and 205D. Major faults of early audions were their inconsistency and their short life. Western Electric was soon to change that; the engineers developed new tubes that were to be used in AT&T telephone repeaters ; they had to be very durable and long lasting.
200 & 201. During WWI engineers from several radio and tube manufacturers made significant technological advances in tube design. In 1920 RCA released tube types 200 and 201. The 200 and 201 were the first radio tubes produced for the mass market. Both were triodes, like Deforest’s Audion containing three components: a filament, grid and plate. The 200 was a detector; the 201 served as an amplifier. In 1923 General Electric came out with the 201A, an equivalent to the 201 but using only ¼ the filament current of the 201; the 200A came out two years later.
199. Like the 201A the 199 used a thoriated tungsten filament. The significant difference between the two tubes was the low battery usage of the 199 tube. The filament used a mere .06 amperes at 3.3 volts compared to .25 amperes at 5 volts. Two years later, in 1925, the 120 was introduced; it provided greater amplification in the final audio stage of a radio.
WD11. Another dry-cell tube introduced by Westinghouse in 1922 was the WD11. The WDll had a filament designed to be operated from a single 1.5 volt battery drawing .25 amperes at 1.1 volts. The base of the WD11 was different from previous tubes; it had long pins but only one fat pin. In 1923, a version of the WD-11 having a standard “UV” base was introduced, the WD12.
AC Radio Tubes. The UX226 and the UY227 were a breakthrough for radio set design because they could operate off of AC rather DC current. They help lead to the introduction of radios that could plug into the wall socket and operate off of standard household current.
24A Screen-grid Tube. The next step in AC radio design was the introduction of the screen-grid tube. The first screen-grid tube generally available in this country was the type 22 introduced by RCA. The 22, which was a battery tube, soon faded because of the blossoming of AC-operated sets. The type 24 quickly replaced the 22; it was introduced in May, 1929. The 24 was a tetrode containing a cathode and a 2.5-volt heater similar to the 27 tube and like the 27 used a 5 pin base.
Metal Tubes. In 1935, RCA introduced tubes with metal shells instead of glass. A number of the first metal tubes introduced were remakes of existing tubes but now using the brand-new eight pin octal base.
Miniature Tubes. Miniature tubes were first introduced in 1940. The new tubes were tubular with a tip seal and allowed radio manufacturers to produce smaller radios.
I have skipped over many important events in the development of radio or audio tubes; nevertheless it is hoped that this quick summery of the development of tubes in the US will give readers a glimpse of the richness and diversity of tubes.
Howard Stone
StoneVintageRadio.com
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