Radio Broadcast (Nov 1926-Apr 1927)

Audio Channels for the Browning-Drake Receiver A Letter from Qlenn H. Browning, the Co'Designer of the Well-Known ' Browning-Drake Receiver — How the Different Forms of Audio Amplifiers, Transformers, Resistance, Impedance, and Dual-Impedance, M.ay Be Used — An Output Device for the Browning-Drake Receiver •"■LENN II. BHOWMNG Oetooer 6, 1926. Mr, J, B. Brennan, c/o Radio Broadcast, Cardan City, B. T. • Bear Mr. Brennan i I enjoyed reading your article, "The B. B. Impedance Coupled. Browning-Drake'* in the September Hadio Broadcast. The receiver described in that article has been oarefully designed and It presents a good and symmetrical appearance. I was glad to note the placing of the tubes to provide quite short leads, as the success or failure from the home constructors1 point of view depends largely upon the way the radio frequency part of the circuit Is laid out. It will Interest you to know that I have found that a considerable misunderstanding exists about the various models of BrowningDrake receivers which have been brought before the public. In Justice to the many present and prospective users of Hie Browning-Brake, it seems necessary that some effort be made to clear up this confusion. Mr. P. H. Drake and myself developed a new type of radio frequency transformer, which is believed to be nearly as efficient as Is possible to design, and placed It In a circuit consisting of a directly coupled antenna tuning system, one stage of balanced tuned radio frequency amplification and regenerative detector. Thus the circuit called the Browning-Drake consisted only of this. Of course, different types of audio may be applied to any type of receiver, and the Browning-Drake is no exception. The fact that a different audio combination is used doeB not necessarily mean that the receiver has been improved. It Is really confusing to find that one type Is designated as better than another, as the efficiency of the complete set depends almost entirely upon the efficiency of the radio frequency amplifier and detector. I would suggest, that as a service to the readers of Badlo Broadcast, you publish the simple two-tube Browning-Drake receiver circuit together with all the various forms of audio-frequency amplification which are in use today. « Very truly yours, GHB'HC GLENN H. BROWNING VERY few circuits have enjoyed the widespread and well-earned popularity accorded the Browning-Drake circuit. This circuit has much in common, electrically, with the Roberts Knockout receivers described for many months in various issues of Radio Broadcast. There is no certain way of estimating the number of Roberts receivers built throughout the country, yet there is little doubt that the number is more than 200,000. In the case of the Roberts circuit, it was basically never materially changed in design from that described in the original article written by Doctor Roberts, which appeared in Radio Broadcast in March, 1924. The Browning-Drake circuit equally popular, too, has remained practically unchanged since the first descriptive article. And like the Roberts circuit, the work of Messrs. Browning and Drake has been heralded throughout the length and breadth of the country. Mr. Volney Hurd, the genial editor of the radio section of the Christian Science Monitor, has published practically all of the advances made in the combination of the fundamental circuit with various types of amplifiers. This course has been followed by editors of other newspaper radio sections and, recently, numbers of different assemblies, based on the fundamental Browning-Drake circuit, have appeared in various radio magazines. In this magazine, in December, 1924, Glenn Browning described a model of his receiver employing two stages of transformer-coupled audio amplification. Again, in December, 1925, another description of thecircuit was written for Radio Broadcast by Mr. Browning. In this latter article three stages of impedance-coupled audio amplification were added to the basic circuit. This design met the requirements of those who were interested in constructing a model using impedance amplification, which, at about that time, was receiving an increasing share of attention. In the September Radio Broadcast of this year, an unusually complete constructional article described how to put together another model of the impedance-coupled Browning-Drake receiver. The constructional design of this R.B.I mpedanceCoupled Browning-Drake was due to John B. Brennan, technical editor of Radio Broadcast, and was arranged with the advice and cooperation of Mr. Browning. It was designed so as to be as easily and efficiently put together as is possible by the home constructor. Of the excellence of its electrical design, there is no question. Since the public has had many receivers described as "Browning-Drake" offered to it, the Technical Information Service of Radio Broadcast Laboratory has received a large volume of inquiries asking which Browning-Drake set should be built. The many conflicting claims made for the various models left the average radio reader in a highly confused state, and the obvious confusion among the puzzled set constructors has made it necessary to present briefly the basic Browning-Drake two-tube circuit (Fig. 1) together with diagrams showing the various forms of amplification which have been used with it. Each type of audio amplifier, whether it be transformer, impedance, resistance, dual impedance, or combination of any of the foregoing, has its good points and, after the constructor has considered the faults and advantages of each, he is able, as a rule, to choose the type which best fits his needs. To this end, let us consider each type separately, leaving Mr. Home Constructor to choose for himself. FORMS OF AUDIO AMPLIFICATION npRANSFORMER-COUPLED audio ampli*■ fication. i.e., two transformers and two tubes such as is shown in Fig. 2, will give ample volume for loud speaker reception, but unless high-grade transformers are used, the quality or naturalness of received signals suffers somewhat. Three stages of impedance amplification, which requires three choke coils, three blocking condensers, and three grid leaks (or three Impedaformers, which are the equivalent), as shown in Fig. 3, gives almost perfect quality, and ample volume. A three-stage resistance amplifier uses the sameapparatus with the exception that resistors are utilized instead of choke coils. See Fig. 6. It has the property of giving almost perfect quality, though a little less volume, but is naturally a bit cheaper to build, as resistors are less expensive than choke coils. High-mu tubes may be used with either of the above amplifiers, though the ordinary 201-A type give sufficient volume for most purposes. Dual-impedance amplification, which uses six choke coils, three isolating condensers, and three tubes (Fig. 4) is a modification of ordinary impedance coupling. The reason for its existence is that sometimes the audio tubes have a ten