Radio Broadcast (May 1928-Apr 1929)

IN THE RADIO MARKETPLACE News, Useful Data, and Information on the Offerings of the Manufacturer The Remler "29" Super-Heterodyne Receiver THE Render "29" is a super-heterodyne receiver intended for use with a short antenna which may be of either the inside or outside variety. The receiver incorporates a stage of screen-grid radio-frequency amplification followed by a regenerative first detector, an oscillator, three stages of transformer-coupled, screen-grid, intermediate-frequency amplification functioning at a frequency of 115 kilocycles, a second detector, and a suitable audio amplifier. The circuit diagram is given in Fig. 1. The major function of the radio-frequency stage preceding the first detector is to increase the selectivity. The screen-grid tube is used in this stage of radio-frequency amplification because of its inherent stability of operation. The intermediate amplifier of the " 29" employs three tubes of the screen-grid type. Although the screen-grid tube is theoretically capable of providing a gain of 40 or 50 per stage, in no case has such gain been obtained in practice and the necessary degree of selectivity maintained. However, both the gain and the selectivity of the screen-grid intermediate amplifier are far greater than could be obtained from an amplifier employing tubes of the 201 a type even if excessive regeneration were used. The gain per stage has, however, purposely been held down somewhat in order to eliminate excessive tube background noise and to maintain the degree of selectivity deemed necessary under present day conditions. Tubes of the 201a type are used for the oscillator and for the first and second detectors. Both detectors are of the leakcondenser type. The regeneration employed in the first detector circuit is obtained by inductively coupling the plate and grid circuits of the tube by means of a third winding or tickler coil, La, The degree of regeneration is controlled from the panel by means of a Chassis view of receiver with shield covers removed This section of Radio Broadcast is devoted to describing the uses of apparatus on the market. In this category fall kits from which receivers and power units may be assembled, descriptions of the uses of parts and accessories which may be announced by manufacturers, and practical information of value to the serviceman, custom set builder and experimenter — all of whom are interested in keeping abreast of what is going on. This month, the excellent kit receivers of Remler and Hammarlund-Roberts are described. — The Editor. 2000-ohm variable resistor, R1; which is shunted across the tickler coil. Maximum regeneration is used only for the reception of distant stations for which a slight sacrifice Power-Suply unit for the Remler "29" in quality of reproduction is permissible. For high-quality local and semi-distant reception the regeneration control should be retarded. The heart of the Remler "29" is the No. 712 screen-grid selector-amplifier. This unit incorporates within a single heavy copper case the radio-frequency and intermediatefrequency amplifier tubes, the transformers, the oscillator and the two detectors. Each individual circuit is, in turn, fully shielded. Such shielding of the individual stages is necessary because of the high gain obtained per stage. The amplifier unit is completely wired at the factory and colored leads extend from it for connection to the panel controls, the tuning condensers, the audio components, and the battery cable terminal block. The intermediate transformers are peaked at the factory and vernier adjustments are provided so that differences in tubes or misalignment due to rough handling during shipment may be compensated by the builder of the set. FOUNDATION UNIT Custom set-builders have in the past occasionally run into trouble due to the improper location of radio-frequency components and wiring. In the design of the Remler "29" great care has been exercised to make the construction such that these difficulties can not arise. All component parts of t he "29" are to be mounted by the builder on a pressed-steel chassis which is included in the No. 752 foundation kit. In addition to those parts mounted directly on it, it supports a pressed-steel panel to which are fastened those instruments controlled from the panel. The instrument panel, the escutcheon plate, and all necessary binding posts, phone-tip jacks, brackets, insulating washers, control knobs, screws and nuts are packed with the foundation kit. There are two major tuning controls which operate, respectively, the Remler Type 632 two-in-line condenser, Ci and C>, controlling the radio-frequency amplifier and first detector circuits, and the Remler Type 638 condenser, C3, controlling the oscillator circuit. A • february, 1929 page 267 #