International projectionist (Oct 1931-Sept 1933)

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December 1931 INTERNATIONAL PROJECTIONIST 25 A SERVICEMAN'S DIARY ADD to your list of "Things We Never Knew Before" (and, in fact never even suspected), the following interesting bits of information gleaned by Editor G. K. Rudulph for his RCA Photophonews. The stories had their inception with servicemen, yet at this season of the year we have charitable feelings even toward servicemen. Witness: "Red rust found on sound head parts in the theatre at Port Orchard (Oregon), was attributed to salt sea air. However, other equipments — also at seaports — were not similarly affected and an investigation was made. Lubricating oil containing acid was eliminated when it was found that bright steel parts in the motor drive side of the heads were not rusted. It was noticed, in fact, that all corrosion occurred on parts exposed and liable to contact by the projectionists' fingers in course of 'threading-up', etc. A litmus test of the operator's skin showed excessive acid perspiration." A serviceman in the Dallas District reported changeover relay, tube sockets, terminal strips, bearings, etc., in one theatre had been penetrated with dust. It was found, as the cause, that the cement floor in the booth perpetually flakes off in dust. Another case reported the corroding of all electrical contacts. After an investigation it was found that the exhaust gasses of automobiles parked outside the windows entered the room and thereby became the corrodent. Solution: 30 X .1 v. = 3 volts (after 1st tube) 3 v. X 30 = 90 volts (after 2nd tube) 90 V. X 30 = 2,700 volts (after 3rd tube) In brief, the overall amplification of any amplifier is determined by the following formula: ^ ;_ A = e X (/i)n A = overaH amplification e = impressed voltage fi = amplification factor n = number of tubes The term "p." means that the amplification factor of the tube is multiplied by itself as many times as there are tubes. For example: (1) With .1 volt and with one tube, the formula gives us: A = .1 X 30^ A = 3 volts (2) With .1 volt and with two tubes, we get: A = .1 X 30' A = .1 X 30 X 30 A = .1 X 900 A = 90 volts These calculations could go on for a great many tubes. In calculating for many tubes, however, one must take into consideration tube noise and other extraneous capacity and coupling effects which introduce elements of noise which are amplified along with our original voltage. Voltage Drop A power supply delivers 500 volts of direct current which has been properly rectified and filtered from the A. C. supply. Problem : A 30,000-ohm voltage divider is connected across the output. At what points may taps be taken so as to produce voltages of 90, 180, and 230 volts, respectively (Fig. 7). (Hint: The larger resistor will have the greater voltage drop.) Solution : 90 180 230 500 (1) H h = ;or 500 500 500 500 9 18 23 50 (2) H h = 50 50 50 50 Since there are 50/50th parts in 30,000 ohms, each l/50th of the resistor is equivalent to 600 ohms. Therefore: (1) 9 For 90v: x 30,000= 5,400 ohms (2) For 180 v: (3) For 230 v: 50 18 50 23 X 30,000 = 10,800 " X 30,000 = 13,800 " 50 50/ /50 {To be continued) 30,000 " Harland Holmden, B. A. of Cleveland Local Union 160, has been appointed seventh vice-president of the LA. to fill the vacancy made by the resignation of President William F. Canavan, Holmden's appointment is effective immediately. TELEVISION SECURITIES THE following summary concerning several of the leading television companies is being distributed by a New York investment securities house which specializes in television securities, and will undoubtedly prove helpful to those interested in this art: Jenkins — Incorporated in 1928 to promote ideas and patents of C. Francis Jenkins. Controlled at present by the De Forest Radio Co. Company is offering a television set for the home and has been operating television broadcasting studio for some time. Stock was sold in 1928 for $10 per share. Now on the N. Y. Produce Exchange and selling for about $2.50. Standard — Company has taken over the Insuline Corp. of America which manufactures electrical parts and is offering television home sets priced from $37.50 up. Capitalization is for 1,000,000 shares of $1 par value. Insuline Corp. reported profit for nine months ending July 31, 1931 of $38,653.75. Factory is located at 23 Park Place in New York City. Stock is offered at $2.00 per share. Baird — Company is an English company which is offering a television home set and operates a television broadcasting studio. A recent announcement wa& made that the company intends to offer a set in the United States to retail for $25.00 and has made arrangements for broadcasting with station WMCA in New York. Shares are listed on the London Stock Exchange and can be bought here for about 85c. Telephoto & Television — Incorporated in 1929 as the Telephoto Corp. to manufacture photo-electric cells and television tubes. Company has been supplying its products to Paramount-Publix, Universal Sound System, and others. The photo-electric cell, called the "eye" of television, has many other uses which gives the company several outlets for its sale. Company can supply kino-lamps and cathode-ray tubes for television receiving sets. Stock was offered recently for $2.50 per share and is now selling for $3 on the N. Y. Over-The-Counter market. President is Mr. Nicholas Fabian, who was President of the Televocal Corp., manufacturing radio tubes, which company was bought by the banking firm of Lehman Bros, in 1929. Shortwave & Television — Company has its headquarters in Boston. Mass. Offers a television kit and set and operates a broadcasting studio. Also sells a shortwave radio set. Stock is on the N. Y. Produce Exchange selling at about $2.00. The television field generally has been very quiet for the past six months, with the exception of the recent Sanabria demonstration in New York.