the instruments and bulbs are sold and licensed for only one purpose, but because the operator is looking for “something for nothing,” which is impossible in the long run.
There are many operators of experience with the Audion who know of all the above points, and many more who do not, and these suggestions, the result of long and active experience of one who has corrected more Audion troubles than perhaps any other one individual, should be given that close attention and careful consideration which they deserve, that the very best of results may be obtained and the longest possible ranges covered.
BLUE DISCHARGE OF GLOW
This appears in some Audion Bulbs and not in others. If allowed to persist, the vacuum automatically increases. For this reason the glow should not be allowed to appear and certainly not to continue, as the vacuum may rise to a very high value, requiring very high voltage in the “B” battery. Many amateurs cannot seem to comprehend the value of instructions of this kind, and if they ruin bulbs in this way, always claim that the bulb “was defective,” although it is their own negligence which caused the condition.
A super-sensitive detector like the Audion should be handled and used with reasonable care and intelligence. It is not “fool-proof.”
One of the most essential points very seldom appreciated or even known by most operators is the fact that a very fine regulation of the “B” or high voltage battery potential is extremely important in securing utmost efficiency with the Audion. A difference of one volt may make a difference in range of as much as 25 per cent.The amateur types of Audion Detector manufactured until 1916 have a switch adjustment for this high voltage, providing at each step a difference of three to four volts, The Audion Bulbs were, of course, and still are tested on this type of instru-
ment, so that they may operate properly with same.
One kind of “trouble” is due to the fact that after an Audion Bulb has been used for a time, the vacuum changes slightly, so that the correct voltage required becomes slightly different in value.
Now, it can be readily understood that the operator will have difficulty in obtaining best results when this occurs, because with the switch on one point, the voltage is too low, and on the next higher point, it is too high, and the hissing sound in the telephone receivers may drown out the incoming signals.
The purpose of replacing the “step by step” switch by a potentiometer, which has been done in the new instruments, is to overcome this difficulty and provide any desired voltage within the limits of the battery.
For the benefit of the large number of operators whose Audion Detectors are provided with “step by step” high voltage control switches, the following is recommended on account of the difficulties certain to be encountered, even if the potentiometers were furnished them, in installing, same in their instruments.
If a small box is made, large enough to hold one 3 cell flashlight battery, and a switch is mounted on the box, and arranged to cut in one cell at time, and this device is connected in series with the telephone receivers, and the receiver binding posts on the detector, a very satisfactory adjustment will be provided, enabling the operator to accomplish excellent results with bulbs otherwise considered less sensitive than standard. Of course, this extra battery must be connected in circuit in the proper direction, so that it acts with and not against the regular high voltage batteries of the detector. The proper direction can be readily determined by trial.This arrangement is thoroughly recommended to every user of an Audion instrument. It is certain to produce results far superior to any ever previously obtained.
Page:March 1916 QST.djvu/5
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