Radio Broadcast (Nov. 1925-Apr 1926)

700 RADIO BROADCAST ADVERTISER The AmerTran DeLuxeis made in two types, a first and second stage. Price, either type, $10.00. j\ flew Standard of Excellen ce in AudioAmplifica tion The realism of this new audio transformer is outstanding. Realism of this kind results from the uniform amplification of the fundamental tones of the lower register. The AmerTran DeLuxe makes possible the natural reproduction of not only the Overtones, but all of the trans' mitted Fundamental tones. I AmerTran Power Transformer type PF-45, Price $15.00, type PF-52, Price $18.00. The AmerChoke type 854 is a choke coil or impedance of general utility. Ptice $6.00. A Qood Audio Amplifier Requires enough plate and grid bias voltage on its tubes to prevent them from being overloaded by the signal voltage. The AmerTran PF-45 or PF'52, with the half wave high voltage rectifying tubes now available and suitable condensers and resistances— together with three AmerChokes Type 854 will furnish these proper voltages. This combination will give real quality loudspeaker volume. AmerTran Power Transformers also sup' ply A. C. filament current for the last audio tube. . AmerTran Audio Transformers type AF6 (turn Ratio 5) and AF7 (turn ratio 3V2) are the leaders in their class. Price, either type, $5.00. Write for booklet describing these and other AmerTran Products — with recommendations on their use. It's free on request. All prices are F. O. B. Newark, N. J. AMERICAN TRANSFORMER CO. 178 Emmet Street, Newark, N. J. "Transformer builders forever twenty-fire years" Sold Only at Authorized AmerTran Dealers. Fig. 7. then the minimum capacity of the circuit is calculated by the following formula: C= Ci C2 ivhere C, equals the minimum capacity of the variable condenser (.000025 mfd.) and Cs equals Min. .000025 mfd. Max. .0005 Ci c2 .0005 mfd. Ci Cz '•< C 5^' FIG 7. the capacity of the fixed condenser, stitution in this formula, we get: By sub .000024 mfd. ~^ .0005 The same formula may be applied for finding the maximum capacity of the arrangement, the maximum capacity of the variable condenser being substituted for Q. AN IMPEDANCE-COUPLED AUDIO AMPLIFIER FOR a means of amplifying audio frequencies, the impedance method is commendable because of its simplicity of connection, and also because use can be made of discarded transformers or other coils. From the circuit in Fig. 8 it will be seen that all that is necessary for a coupling agent between the regenerative detector tube and the first audio tube, is a coil having an iron core. Of course, this coil unit should have certain definite dimensions for most efficient functioning, but it has been found that such coil units as the secondary of a transformer which has been rendered useless by a burned-out primary, or the wire-wound bobbins of discarded head phones, are satisfactory makeshifts for an amplifier unit. The connections for an entire receiving circuit, showing the application of an impedance or choke coil to it, are clearly indicated in the accompanying circuit diagram. The two tuning units in this circuit are standard coupler units. In the antenna unit, the secondary coil is tapped at the mid-turn for the filament return connection. Rice neutralization is employed. The neutralizing condenser is connected between the plate of the radio frequency tube and the lower end of the first coil-unit secondary. These connections are clearly shown in the diagram. The value of the neutralizing condenser is .000016 mfd. The tuning condensers are both about .0005 mfd. The similarity between impedance and resistance audio amplification is apparent from a glance at the circuit diagram. In resistance amplification a resistor of approximately 100,000 ohms is substituted for the impedance coil, and there is a B battery voltage drop across the plate resistance. Any variation in voltage causes a corresponding voltage variation in the resistor, and these voltage variations are applied to the grid of the succeding tube, and magnified by the latter's action. For an impedance amplifier, the general action is much the same, with the exception that, instead of utilizing the voltage drop across a resistance, the variation in voltage across an inductance is used. It is essential that the isolating condenser C, should be of the highest quality, one of mica dielectric being recommended. CHOKE OR IMPEDANCE AUDIO AMPLIFIER FIG. 8 GRID INQUIRY BLANK Editor, The Grid Radio Broadcast Garden City, T^ew Tor\ Dear Sir, Please give me the fullest information on the attached questions. I enclose a stamped envelope. I I I am a subscriber to Radio Broadcast and therefore will receive this information free of charge. I I I am not a subscriber and enclose $1 to cover cost of answers. Name . Address . G. A. ■fa Tested and approved by Radio Broadcast fa