The Birmingham age-herald., 1922-08-13
HOW ID PROLONG THE LIFE OF A
 VACUUM TUBE
Useful Hints in Operation Which Will Increase It's
 EffiCienCy--Burn Fila { ment Carefully

 
 The most expensive instrument in a radio receiver is the vacuum tube, and at the same time it is the most fragile. For this reason the radio fan Bhould take every precaution that he gan to care for it and prolong it's period of usefulness.
 It is my intention in this article to outline some of the simple precau- tions that can be taken, which will permit the best possible results being obtained, while at the same time per- . hitting the tube to operate for the longest possible time that it can.
 The most important part of the tube is the filament. This is the ele- ment that throws off the stream of eleetrons that perform so important The electrons are thrown off by the filament when 1t is heated by the current from suitable battery. The electrons themselves are controlled by the grid of the tube, and the out put O. the tube is from the plate eircuit.
 Critical Point in Tube
 There is a peculiar factor about the Vacuum tube and it is this: The more the current is turned on and the brighter the filament glows, the greater will be the number of cleo irons that will be omitted until cer- tain point Is reached, and then no Snatter how much the brilliancy of the filament is increased, there will be no further increase in the flow of electrons. This is known technically ps the saturation point, and also the eritieal point.
 The result is that when the fila ment is burning brighter than what Is known as the "critical point" the life of the tube is being shortened without any corresponding increase in efficiency. In fact the efficiency of the tube is really decreased. Therefore. 1t will be readily seen that to increase the brilliancy of the tube is of no value whatsoever and is merely burning up the filament and current from the battery.
 Some radio fans have devised an , arrangement of switches. whereby they can connect or disconnect the "A" and "B" batteries at will. This is a very good idea, and is designed for the purpose of reducing the num- Der of adjustments necessary in op- erating the set. Its chief purpose Is to throw on the switches and then have the music come in immediately.
 System Has a Drawback This system, however. has very serious drawback. It lies in the fact thdl every pdIleTyt dller d peTlOd OI : rest recuperates slightly, and when ' it is placed into circuit again will, at first, give off more current than 1t did at the time that 1t was discon- nected from the set. The consequence is that when the switches are thrown on the tubes really get a little more current than they usually do, and so what is gained in reducing the num- Der of necessary adjustments Is lost nd nf fbn Ike battery. It is best to turn the rheo- stats back little before turning on the current.
 In a recent issue of "wireless World" an English publication, W. N. Buchanan, Jr., makes a suggestion that is based upon some very clever reasoning. He suggests that the two tube socket should be connected to the double pole double throw switches so that the two terminals can be reversed in polarity, so far as their connection with the batteries is concerned. He makes this suggestion upon the following reasoning:
 Electrons Are Negative
 It is a fundamental fact that in Vacuum tubes the filament emits electrons and that the number of electrons emitted will be greatly in- creased if plate is inserted in Vacuum tube and given a positive po- tential. Put in simple language, this means that when you connect your "B'' battery to the plate terminal of your vacuum tube you are placing thereon high potential, compared with that of the filament. As elec- irons are negative corpuscles of elec- trfcity, the positively charged plate attracts the electrons to It. MT. Buch- anan reasons, therefore. that the emission must be from the side of the filament to which the negative termi- nal of the storage battery is con nected, and that very little emission, If any, takes place from that side pf the filament which is connected 10 the positive plate of the storage battery.
 Having assumed this, he then points out that the negative side of the filament is naturally subjected to the severest strain and will give out much quicker than the side which is consequently connected to the posi- tive plate of the battery. He argues. therefore, that if a suitable change over switch Is connected to the cir cult the two sides of the filament will be subjected to this strain whenever they are connected to the negative side or the battery. and in this man ner the strain can be applied much
 
 tube increased to double the amount. that it would be under normal cir cumstances.
 Regulate Plate Voltage
 Another point which should be carefully observed in the operation of a vacuum tube is the amount of plate voltage that is applied to the plate. There is a point (which is also criti- cab. beyond which it is not safe to go. Fortunately, 1t is very easy to determine just how much plate vol tage vacuum tube will stand.
 If the voltage applied to the plate is too great for the tube, a very pro- nounced blue glow will appear inside the vacuum tube This Is the danger signal, and it should not be ignored under any circumstances. As soon as it is seen, the storage battery should be disconnected from the tube. (This can be done by shutting down the rheostatI and the one of the 22h volt units in the .B" battery should be taken out of the circuit entirely.
 It i5 not bad idea to use one of