Radio today (Jan-Mar 1939)

give* tfou HIGH OR LOW PITCH WITH THE SAME MICROPHONE With the flip of a finger you can now(l)lower or raise the response of the microphone. . . (Z) adjust the microphone for most desirable response for close talking or distant pickup. . . (31 adjust the system to any "taste", room condition, or equipment. MODELS RBHk, BBMk, with Acoustic Compensator.irequency range. 40 to 11000 cps, output, -65 db., complete with switch, cable connector* and 25' of cable $42.00 LIST NEW! MODEL RSHk (hi-imp); HBSk (200 ohms) Frequency range 60 to 8000 C.P.S. Output -68db. . . . Chrome or Gunmetal ......... ...... .$32.00 LIST NEW LOW-PRICED CONTACT "MIKE" $12.00 LIST The new popular-priced Amperite Contact Microphone can be used on most radio sets made since 1935 and on all P.A. systems. It "makes an ordinary violin sound like a Strad" . . . gives a small piano the tone of a Grand. And yet, there is no distortion. No unnafuraf ettects. No "fingering noises." TVo changes in strings or instrument. Attached without tools. Operates with either high or low gain amplifiers. Has frequency response of 40 to 9000 cps. Output, -40 db. 20' of cable. MODEL SKH (Hi-imp); SKL (200 ohms), $12.00 LIST Professional Model KTH (or KTL). .$22.00 LIST ^NEW COMPACT "MIKE" A new velocity microphone of compact size, having a head only l'<i"x 23/s"xl%." Good for speech and music. May be used as hand mike as well as for stand mounting. Complete with output transformer, cable connector and switch. Output, -70 db. into open line. Frequency response 60 to 7500 cycles. MODEL ACH (Hi-imp.); ACL (200 ohms) $25.00 LIST MODEL RAH.. .$22.00 LIST PJL Men, you can improve those "price" jobs by using the popular Amperite Model RAH (or HAL). You will get better results because (1) it is excellent for both speech and music; (2) has flat response without undesirable peaks; (3) reduces feedback; (4) stands up under rough handling and changes in temperature, pressure or humidity. . . . Frequency range 60 to 7500 cps. Output, -68 db. MODEL RAH (Hi-imp); with 12' of cable; RAL (200 ohms) with 8' of cable, ONLY $22.00 LIST Write for Complete Illustrated Bulletins and Valuable Sales Helps. 561 BROADWAY N. Y Cable Address: Alkem. New 1 MICROPHONE Amperite (o. SERVICING sistors) so that the approximate resistor size can be determined. For example, let us assume a case where the actual resistor watts is 10 and the maximum temperature attained is to be 310° F. Subtracting an assumed ambient (room) temperature of 70° F., the temperature rise is 240° F. Assuming the resistor to be mounted in free air, the intersection of a horizontal line at 240° F., and the "IN FREE AIR" curve occurs opposite a multiplying factor of 2.5. Hence, a resistor of 2.5 x 10 watts or 25 watts rating is required. This happens to be a stock size and the dimensions of the core are %6" x 2", for this example. Enclosing a resistor so that the air circulation is restricted raises the temperature for a given watt load markedly. The exact amount depends upon the shape, size, surface, color, etc. of the enclosure. The graph is for a typical condition. Note that for the same 10 watt load, and 240° F. temperature rise as before, a %6" x 4", 50 watt rating, resistor is required when enclosed instead of the 25 watt size for free air. For equal temperatures, an enclosed resistor must ordinarily be at least twice as large as when operated in free air. HOW BEAMASCOPE OPERATES The Beam-A-Scope is a shielded loop antenna designed for noise reduction. This is accomplished in three ways. In the first place, the well-known directivity of the loop is used, the loop being rotated so that the principal source of noise is in the direction of zero response of the loop. In the second place, the shield around the loop removes its capacity to ground (See Fig. 1), so that noise, which would otherwise be picked up in the ground return path, is eliminated. In the third place, the shield, by eliminating electrostatic pickup, makes the loop insensitive to the strong electrostatic field which is present around all noise sources of the dipole radiator type. The electrostatic shield around a loop in a Beam-A-Scope is cylindrical in form, the ends being two metal discs, and the side consisting of a woven material in which the vertical threads are metallic. All the vertical threads make contact with the top disc, but only one makes contact with the bottom disc. In this way there are no closed conducting circuits parallel to the loop, so that the Q of the loop is not damaged and the magnetic pickup of signals is still possible. Ordinarily the sensitivity of a loop would be small, but in the case of the Beam-A-Scope the sensitivity of a normal indoor antenna is retained, because the loop is tuned and has a high Q. Since the loop size is determined in the design of the receiver, the condenser which tunes it can be ganged with the condensers of the RF and oscillator circuits. Besides the noise reduction obtainable with a Beam-A-Scope, there is also the additional, very practical advantage that no external antenna or ground connection is required. ADAPTING TRIUMPH TESTERS FOR SINGLE-ENDED TUBES To accommodate the new 6sQ7 tubes, all Triumph Model 420 and Model 430 Tube Testers should have the following additions made in their wiring: Terminal No. 1 of the special octal socket should be connected to terminal No. 1 of the standard octal socket, and terminal No. 2 of the special socket should be connected to terminal No. 8 of the regular octal socket. This additional wiring brings these testers strictly up-to-date. Model 430 with serial numbers above 1056 are factory wired to accommodate the 6SQ7 tubes. New tube index charts are available. PORTABLE SERVICE LAB Exceptional ingenuity and craftsmanship, as well as utility, are incorporated in a novel rolling Radio-X-Ray Service Lab. constructed by Ernest Moore, a leading radio technician who operates his own modern service shop at Chickasha, Oklahoma. In order to impress both his cus •--©- STRAIGHT WIRE ANTENNA NO PATH TO ANTENNA FOR _ _TNQ1SE^ BEAM-ASCOPE By electro-statically shielding the loop in the G-E beamascope receiver, local noise pick-up is eliminated because there is no noise path to the antenna. 42 Radio Today