Radio Broadcast (Nov. 1925-Apr 1926)

358 RADIO BROADCAST ADVERTISER SUPER S $25.00 Rubber horn 14V diameter. Black mat finish. Gold decorated base. Equipped with new Super-Unit. TONE clear — natural — pleasing — musical ' I VHE latest Bristol refinement, the Super-Unit, contains a large, low-pitch diaphragm which brings in, not only the middle and upper registers, but all those deep bass notes heretofore only imperfectly heard if at all. With a Bristol, either Super S or Super C, you hear all the concert; with it all tones are distinguished in their proper qualities, in all selections. Have Your Dealer Send One Out On Christmas Eve He will be glad to have you try any one of the Bristol models in your home. It's an ideal way to appreciate Bristol tone quality and judge for yourself. There are four Bristol Speakers: Super S at $25.00, Super C, the Cabinet, at $30.00 and horn types at $15.00 and $20.00. Send for Booklet "How to Select Your Loud Speaker" Easily understood and explains the " how" and "why" of mechanisms and materials in loud speaker construction. Bristol Speaker [The AUDIOPHONE1 THE BRISTOL COMPANY Radio Div. AH WATER BURY, CONN. for 36 years makers of the highly sensitive and accurate Bristol's Recording Instruments. Therefore, by placing one resistance in series with and common to all the neutralizing circuits, the capacity of each can be changed by varying this common resistance. The effect is to unbalance these circuits, permitting an increased sensitivity, easily variable over all frequencies within the range covered. Here again we find a fortunate factor operating in our favor. Aside from the advantage of enabling us to control several stages with one knob, this resistance does not introduce losses or interfere with selectivity, and in addition to that it does not affect dial readings by detuning the circuit. DUAL RESISTANCE-CONTROL AN ASSET INASMUCH as sensitivity is not required * on stations where it is desirable to reduce volume, the same knob can be used to operate a separate resistance in the B battery circuit to control volume. This is accomplished by a dual resistance containing two distinct resistance elements, each operable over an arc of 240 degrees. When sensitivity is the objective, no reduction in volume is desired. When a decrease in volume is wanted, there is no demand for sensitivity. Therefore, in operation, it is necessary only to turn one knob to the right or left to secure either one or the other as desired. In addition to the simultaneous unbalancing feature which makes it possible to secure sensitivity over the full range, the "Counterphase" method makes it possible to control three stages of tuned radio frequency efficiently with but two tuning controls. In design the circuit is distinctly new and will no doubt appeal to those who are of that jaded group of circuit seekers and dyed-in-the-wool experimenters who are always on the look-out for "something new under the sun." VALUES OF PARTS EMPLOYED IN CIRCUIT THE coils employed in the "Counterphase" circuit are toroids, each wound on a frame if -inches square. The secondary consists of 168 turns of No. 24 double silk covered wire and is tapped at the 124th turn from the filament end. It has an inductance value of 220 millihenries. The primary is spaced inside the secondary at the filament end, and consists of 52 turns of No. 36 d.c.c. or d.s.c. wire. The "Counterphase" coil is wound with 96 turns of the No. 36 wire, its turns being spaced between the turns of the primary. The antenna secondary is tapped at the 2nd, 8th, 25th, and 40th turn from the filament end of the coil. The tuning condensers are .00035 mfd; the trimmers .000024 Tnfd. The "Counterphase" condensers Cn have a minimum of 1 mmf. and a maximum of 30 mmf. The dual resistances are variable, the one located in the counterphase part of the circuit is 3000 ohms and that in the plate circuit 500,000 ohms. The by-pass condensers are as follows: — A .00 1 -mfd. across the first audio transformer primary; a i-mfd. across the C battery, and a i-mfd. across the B battery. Tested and approved by Radio Broadcast