Page:March 1916 QST.djvu/4

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MARCH, 1916
43
QST

efficiency. A crystal operates whether exactly in tune or not, but the Audion being potentially operated, must have efficient tuning equipment if its advantages can realized to the fullest extent.

 (6) Do not try to use a fixed condenser in series with an Audion Detector. Every one of these instruments has a special mica condenser within it, properly connected and built, and I do not believe it can be improved upon. Unauthorized parties give all kinds of advice, but it seems only reasonable that the manufacturers should know and install what is right.

 A variable condenser across the tuner posts is of great value in obtaining the exact point of resonance, but nothing in the way of a condenser should be used in. series to reduce efficiency

 (7) Then there is the operator who turns off his lighting battery and neglects to cut in more resistance by means of the rheostat. The battery recuperates while standing and when turned on again, often burns out the filament or seriously injures it. Remember that a sensitive and delicate instrument requires a little thought and care.

 (8) The use of a magnet near an Audion Bulb sometimes increases the intensity of signals, but we have seen filaments literally bent out of place due to this, and a common result is short life of the bulb. (Note below under Fallacies (3).

 (9) Remember that all regular Audion Bulbs have 3½ volt filaments and never connect more than 6 volts to it. The rheostat will handle effectively 6 volts, but no more should be employed.

ADJUSTMENT OF THE AUDION

 (1) Nearly every Audion bulb has two critical points. One is found when the “A” and “B” batteries are adjusted to certain points. The other is found, generally with the “B” battery adjusted to a higher voltage than above and the filament operating at less brilliancy with the lighting battery connections reversed. Some bulbs have only one critical point, within the limits of the usual “B” battery voltage, and so it is important to TRY REVERSING THE LIGHTING BATTERY connections to the detector.

 An Audion should always be operated with the higher “B” voltage and lower filament intensity to obtain greatest life.

 (2) The critical point is reached at certain adjustments of both the “A” and “B” batteries. At this point, a hissing sound is generally heard in the receivers. If this is present, the filament brilliancy should be decreased until the sound is just
audible or is just below the audible point.

 When strong signals are received, they may be much increased in intensity by increasing both the “B” battery voltage and the filament brilliancy, but while greater volume of sound is obtained, the bulb is not in its most sensitive condition at this adjustment. With some excellent bulbs, no hissing sound can be heard at any adjustment, or it may appear, but be very weak.

 (3) The “Blue Glow” appearing at certain adjustments of the “B” battery in the old style tantalum filament bulbs is often not found at all in the tungsten and Hudson filament types, and is not necessarily an indication of sensitive qualities.

FALLACIES

 (1) Making an Amplifier from a Detector. There are several reasons why this cannot he done with even fair efficiency. If the necessary three winding transformer is not exactly made and balanced, the results are poor. The Audion Amplifier Bulb is entirely different from the Audion Detector Bulb in construction and vacuum.

 The result of trying to make an amplifier from a detector is only a makeshift in which the efficiency is so low as to make it an expense out of proportion to the benefits obtained.

 The Detector bulbs cannot last long enough to make it worth while, and the efficiency, is very low.

 (2) Receiving Continuous or Undamped Waves. Regular Audion Detector Bulbs are not adapted for the reception of continuous waves, because the vacuum is not correct for the purpose and because the filaments must be operated at such a high intensity that they give very short service, making them unnecessarily expensive.

 Then, their use in this way causes,the vacuum to gradually increase until 75 to 150 volts are required for the “B” circuit.

 (3) “Amplifying” Circuits: This is the same old story begun with the creation of the world, of obtaining something for nothing.

 If you will think, you will realize that if you pass through an Audion Bulb or any other apparatus, two or three times as much energy as it is designed to carry, the result will be a short life! This appears in “amplifying” circuits in operation of the filament at excessive brilliancy and in rapid deterioration of the filament from carrying abnormal power. The vacuum increases to an extremely high value in most cases.

 The final result is expense for renewal bulbs far out of proportion to results obtained and general dissatisfaction—not,due to any fault of the manufacturer, because