Radio Broadcast (May 1928-Apr 1929)

RADIO BROADCAST ADVERTISER 57 HFL»Uf With the Wonder Receiver of the Century The Model 10 HFL Isotone SCREENED GRID . . . CUSTOM BUILT . . . RADIO PHONOGRAPH THE HFL Isotone is unquestionably the most * sensitive receiver that the world has ever seen. It will absolutely out-distance all other receivers regardless of price or type ofconst ruction. The amazing sensitivity of the HFL screened grid amplifier remains unequalled. No other commercial amplifier permits a gain of 65 per stage under actual operating conditions. The HFL Isotone is the supreme radio achievement. It's position has been definitely established In radio laboratories the country over. 2000—3000 Mile Range So sensitive is theHFL Isotone that stations over 2000 miles away have to be turned down. Tremendous volume is obtained from stations all over the North American continent. The HFL Isotone will receive any station in the world that is putting enough signal voltage Into the antenna to actuate the first tube in the receiver. . One Spot Tuning ^ The 450 kilo cyle screened grid amplifier allows absolute one spot tuning. Extreme selectivity is gained by hand tuning each transformer with a small variable condenser. An entirely new method of control permits the tubes to be operated in their most sensitive condition — just below the oscillating point. The HFL Isotone will actually select an S kilo cycle band when the amplifier is worked'at maximum. Dual detection (an exclusive HFL development) allows reception of the weakest signals and still permits the undistorted handling of powerful locals. A.C. or D.C. Operation Through the use of an ingenious system of filament control, the HFL Isotone operates perfectly with batteries or the special HFL — A. C. power supply. The same tremendous reserve power is available with batteries. The same crystal clear tones are developed with A. C. Only 130 mils, of plate current are required by the entire receiver including the two power tubes. Phonograph or Radio A special method of switching and ballasting allows an instant choice of phonograph or radio music by simply throwing the master control switch on the front panel. Both kinds of music are so amazingly realistic that no human ear can discern the difference between an original selection and an H F L reproduction. An automatic ballasting shunt — another exclusive H F L feature— prevents audio tube overloading when the six radio frequency tubes are disconnected during phonograph operation. The three stage, push pull audio amplifier is a marvel of electrical design Not only does it faithfully reproduce every musical frequency, but it actu ally corrects the flaws In broadcast transmissions and phonograph records. 45 Minute Construction TheHFL unit method of construction is the sensation of the 1929 radio season. Every item necessary to build a perfect Isotone comes in a factory sealed carton. Each of the three main units is wired and laboratory tested at the factory. Only ten wires are connected by the set builder. An exact, progressive method of assembly eliminates every chance of error. "We stand ready to prove, at any time, that a standard HFL Isotone can be fully constructed in less than forty-five minutes. Absolute Guarantee We guarantee, absolutely, that a standard HFL Isotone receiver operating under favorable conditions will receive over a distance of not less than 1500 miles. We guarantee every HFL unit to be mechanically and electrically perfect. Any unit believed defective will be immediately replaced atnoextracha rge. We reserve the right to select a location and prooe by demonstration that it will receive over 1500 miles Set Builders write for special data HIGH FREQUENCY LABORATORIES 28 North Sheldon Street Chicago, Illinois diagrams and all information Mail this Coupon Today SEND THIS NOW! HIGH FREQUENCY LABORATORIES Office 3 — 28 N. Sheldon St., Chicago, 111. Gentlemen: Without obligation please send your new ISOTONE booklet. Name. Address^ City State Please print plainly