International projectionist (Jan 1941-Dec 1942)

tainty that that tube is impairing thesound. It may be. And it may be doing no other harm than to reduce the volume a little. It should be replaced, but the meter reading does not always mean that any and every trouble under investigation has been found. Complete sound outage, for example, is not likely to be the result of low space current in one tube. — unless the reading is extremely low, and not invariably even then. A moderately low reading is not necessarily associated with noisy sound, or even, in every case, with distortion. It is likely to be related, however, to low volume. In short, sound troubles should be run down systematically according to a pre-arranged plan. It is a mistake — and one likely to add to audience impatience in time of trouble — to assume that the amplifier meter answers all problems. Above is the old type amplifier meter using a numbered dial. Normal reading: It may seem strange to some, but the fact that the meter shows a tube to be good does not always mean it is. The meter, remember, reads only space current. Generally speaking, if a tube has normal space current, it will operate normally. But this does not always follow. It may have normal space current and be noisy. It may also (though this is rare) show normal space current and fail to amplify normally. A "'good" meter reading can be taken as acceptable evidence that the tube is alright, subject however to further investigation and experimental replacement of the tube in stubborn trouble cases. Danger Sign High reading: In an old tube is a sign of danger, and the tube should be replaced at the first convenient opportunity. New tubes, on the other hand, sometimes read slightly high when the manufacturers have built a little extra life into them. High reading in an old tube, however — that is, in a tube that has formerly read lower, needs prompt attention. It may mean some fault in l he amplifier that has lowered grid bias. It may mean excessive plate voltage, possibly due to high line voltage. Either condition is dangerous, since it means excess current is flowing which very possibly will overheat some part of the circuit, resulting in deterioration of some parts, or even in something burning out. High reading may mean a "gassy" tube. This is always true if the tube also shows a blue glow that it never exhibited before. If the blue glow was always present in that tube it may mean nothing, but if it appears after some period of use, and is associated with a higher meter reading, it means the vacuum has deteriorated and gas is present. A gassy tube always distorts the sound more or less — further, the condition may grow progressively worse, with corresponding increase in space current that is dangerous to other parts of the amplifier. Replace the tube as promptly as convenient. Fluctuating reading: The significance of this condition depends on the type of amplifier used. In a Class AB or ' Class B amplifier, working at high volume, it is normal, but most theatre amplifiers that have meters are Class A, and a fluctuating reading means overloading and distorted sound. This may mean that the volume has been run up higher than the system can stand. If a fluctuating reading appears at volume settings which never showed that condition before, look for a tube with a low meter reading and replace it. If the trouble persists, there is a serious fault in the amplifier to be run down and corrected, — except where the line voltage is fluctuating badly, which should be reported to the power company for correction. All of the foregoing refers to conditions under which the meter measures one tube at a time. This is not always the case. Some meters are connected to read current to two or even four tubes simultaneously. Then the interpretation of their action becomes a little more complex. A low reading becomes more important, because it may mean that only one tube is reading low, while the other is balancing the condition by carrying an excessive load. The excessive current through the good tube may overheat or damage something. Replace all tubes concerned till the faulty one is found. A normal reading does not in this case mean that all the tubes are behaving normally. Again, one may be counterbalancing some defect in another. In routine maintenance, use a new tube to replace the working tubes one at a time. Any startling change in reading when this is done will indicate that the tube just replaced was faulty. It need not always be discarded; it can be kept and later matched with another that has the same meter reading, unless it is gassy. A gassy amplifier tube should never be used. A high reading, when the meter reads more than one tube at a time, may mean that one is gassy, or that all tubes are carrying more than normal current because of some undersirable condition, usually high line voltage, which should be corrected even at some cost to the theatre. A fluctuating reading is treated in the same way as fluctuating reading in a single tube. Sometimes there are two tubes in one envelope — double tubes, so to speak. This is common in the case of rectifying tubes, and some amplifying tubes are built that way. One of the twin structures may develop a fault while the other remains normal. Unless the amplifier meter is connected to test each half of a twin tube separately, the projectionist should follow a liberal policy with respect to replacement whenever meter readings depart even moderately from normal, since such departure may indicate that one of the twins is in seriously poor condition, and the other half of the tube is compensating for this by carrying a dangerously high load. Y & W FOR ALTEC Y & W Management Corporation, of Indianapolis, Indiana, has appointed the Altec Service Corporation to take charge of service in the 12 Y & W Theatres in Indianapolis and vicinity. F. C. Dickely negotiated for Altec. The new style meter, above, uses colors instead of numbers, making for quick reading. IA BUYS BONDS Detroit. — IATSE Local B-25, covering film exchange employes, has voted to appropriate S2.000 from the union treasury for the purchase of Defense Bonds, according to Bert Holmes, business agent. 8 INTERNATIONAL PROJECTIONIST