The radio dealer (Apr-Sept 1922)

88 THE RADIO DEALER July, 1922 Saves Vacuum Tube Costs by Doubling Filaments An announcement of interest to the trade was made recently in an interview by M. R. Goldman, of the SelfService Phonograph Company, New York. His statement had to deal with the duplex tube, a form of vacuum tube that does away to a certain extent with some of its expense. " The duplex tube," Mr. Goldman said, " is one of far-reaching importance, and although the duplex tube has been long on the market, only the recent tremendous expansion of Radio has made its true necessity really felt. The duplex tube was patented on April 9, 1918, and patent number 1,262,394 was granted on the basic patent for the single base, duplex filament. Other patents are pending. " The idea behind this novel vacuum tube," he said, " is to put two filaments inside the vacuum where the ordinary vacuum tube has only one. It works the same for the detector tube or the amplifier tube. If one bulb is used to its limits, or burned out accidentally or through fault-" handling, the contacts may be changed and lo ! and behold ! you have a new detector or amplifier." As may be seen from the accompanying illustration his " two-in-one " vacuum tube has two filaments. All that is necessarv to restore a vacuum tube that has suffered a " blow-out " is to change the metal contact at the base of the filament from the dead filament to the remaining live one. The tube is thus ready once more for action. Mr. Goldman asserts that this new tube has met with an enthusiastic response wherever it has been introduced. " In Monrovia, California, and in Albany, in Salt Lake City and in Dallas, this duplex tube has been a remarkable success. Its reasonable initial price and economical features are the cause," he said. The list price of the duplex tube is $8.50 for the detector and $10.00 for the amplifier. Mr. Goldman also intimated that he was at work in launching a new twostage detector set that will be put up in period design cabinets. He expects these models to sell somewhere in the neiehborhood of $150. This enterprising member of the Radio industry is also the distributor of the Rova products, a line of radio equipment that is both complete and reasonablv priced. But Mr. Goldman's chief interest is in the duplex tube and its possibilities of making radio even more appealing to the public by making it cheaper. LETONITE A scientific composition perfectly adapted to RADIO USE KNOBS Of all Descriptions SOCKETS DIALS DETECTOR BASES VARIOMETER Rotors and Staters If it's moulded, we make it Good Deliveries Quotations on Special Work LETONITE MFG. CO., Inc. 1265 Broadway, New York Telephone Pennsylvania 5633 Factory 129th St. and 3rd Ave. DUPLEX Q OTHEK CAT. FEND THE U. S. NAVY GOLD TIP The 30,000 U. S. Navy gold tip vacuum tubes which were originally offered to the highest bidder, same being Jacob Levin, of New York, whose bid was $4.04, are now being offered to the fans at $8 each by the Merchant's Clearing House of America, 610 Broadway, New York City. They advertise " wholesale and retail." RADIO BELLHOPS Paging by radio has been instituted in the Essex, a Boston hotel. There is no longer a " flock " of noisy boys running through the main dining room shouting the names of various guests. Instead, the soft but distinct voice of the telephone operator is sent out to various parts of the hotel through radio devices on the telephone switchboard. Amplifiers in the lounging and dining rooms inform the guests that they are wanted.