Reactivation of Bright Emitter Tubes.

Tubes having thoriated filaments such as 199, 120, 201a, DV2, DV3,DV5 and a few others can suffer from loss of emission due to overload. If you have any of these tubes with low or zero emission they may be quite often restored to good operating condition by the following procedure:-

The tube should first be "flashed" for 10 to 20 seconds at 12 volts for 3.3 volt filaments and 18 volts for 5 volt filaments the filament is then aged at 4 volts or 7 volts respectively for 30 or 60 minutes. If at the end of this time, test for emission and if considered low, age for a further hour or so. Tubes which are really worn out will not respond to this treatment and sometimes the filament will burn out on flashing. I have successfully treated a number of 201As, most of which came up to 80%. My only failure was a 120 whose filament succumbed to the flashing operation.



Hardly an antique valve but a relic of a bygone era.

Vale Thermionic Tube.

Like sailing before the mast the art of the  vacuum tube is almost defunct. As a kid many years ago I acquired my first valve, an A409, with much excitement for my first one valver was ready to put together. I have used many valves over the years and I still enjoy repairing old valve radios. It is very gratifying  that valve collectors are preserving this heritage.

S.T.C. telephone repeater valve type SY 4101D.Made in Australia circa 1929.

Early Marathon AC valve type AC608 made in 1927. This valve was designed for AC filament use has an indirectly heated cathode with the heater connections on top of the outer shell of the base.
A short history of the rise of the vacuum Tube

Our old friend Thomas Edison was the first person to realise that there could be a flow of electrons from a heated cathode to an adjacent anode but he did not recognise it at the time.  During his experiments with carbon filament incandescent lamps he observed a shadow on the glass bulb adjacent to the positive polarity filament support this was due to the emission of molecules from the negative end of the filament being attracted to the filament support which was at a positive potential  and caused a shadow to form on the glass bulb. Edison later placed a metal plate between the filaments and found that he could get a current flow when this support was  positive to the filament but the was no current in the opposite direction. But what to do with this discovery??? Just file it away and call it the "Edison effect".

Ambrose Fleming in the UK studied the Edison Effect and presented a paper in 1890 to demonstrate the ability to send a sensible current between a hot filament and cold anode. By 1896 he realised that this combination of heated filament and anode would rectify alternating current. There was no apparent use for this device at the time and there the matter rested for a number of years.


  Enter now wireless telegraphy and the need for a detector to make the wireless signals audible to the operators. For this purpose coherers and other devices were in use but they were all delicate and erratic in operation. Marconi overcame this to a certain extent with his magnetic detector which was reliable and rugged but lacked sensitivity. In 1904 Fleming decided to experiment with one of his "lamps" and found that he could satisfactorily rectify high frequency currents and from this the diode detector was born.

In the United States Lee de Forrest, after university graduation, worked for Western Electric Company in Chicago. His work took him into the area of detection of high frequency signals and he initially studied the Bunsen burner detector, which proved to be an unsatisfactory device. In 1905 de Forrest had acquired a Fleming valve and arranged for copies of it to be made by the McCandless Company so that he could continue his experiments with detection of high frequency wireless signals. In an attempt to increase the sensitivity of his valves, which were now called Audions, he introduced a grid structure between the filament and the anode to control the flow of electrons. The device worked successfully and a patent application was filed in January 1907, and a patent issued in 1908.The patent application made reference to the possibility of amplification but this facility was not made use of for another few years. Ultimately, in the hands of Western Electric engineers, the Audion was developed as a signal amplifier for telephone repeater services. In January 1915 vacuum tube repeaters were incorporated into the transcontinental telephone line from San Francisco to New York.

: Initially de Forrest's triode had only one anode with a grid structure between filament and anode, one each side of the filament, with two corresponding grids.

 In Europe the French were also developing thermionic valves and one valve in particular, the TM, was copied by the British during WW1 and became known as the Type R, It had a tungsten filament rated 4V at 0.7Amps with anode voltage 30 to 100 volts.

From this point on there was an explosion in designing and manufacturing of valves for an very demanding market and each new series was technically much better than the one before. When valve technology and manufacturing reached its peak the transistor entered the scene and in a very few years rendered the thermionic valve obsolete.

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