Radio broadcast .. (1922-30)

422 RADIO BROADCAST ADVERTISER ANEW and BIGGER Bradleyohm for B-Eliminators Announcing the Bradleyohm-E Perfect Adjustable Resistor for B'Eliminators THE rapid development of B-Eliminators for radio receivers has created a growing demand for an adjustable resistor of high resistance to regulate the plate voltages to the radio set. Bradleyohm-E isanew,large size Bradleyohm of increased capacity and ample range for B-Eliminator service. It is made in several ranges for various types of circuits. If you are building a B-Eliminator, be sure to ask your dealer for Bradleyohm-E of correct range and you will be assured of complete satisfaction regardless of the length of time your B-Eliminator is in service. Mail the Coupon for interesting literature on Alien-Bradley Perfect Radio Devices Allen-Bradley Company 278 Greenfield Avenue Milwaukee, Wisconsin Please send me your latest literature on Allen-Bradley Perfect Radio Devices including the Bradleyohm-E. Name Address. . . fine hacksaw blade will cut a slot of just this width. The depth of the slot will have to be &", or more, according to the gauge of wire used for the primary winding. To take the ends of this winding, fit two small terminals near the center of the form. I say small intentionally, for even slight amounts of metal within the field of a coil tend to reduce its efficiency. These terminals are very convenient, since connections to the bus bar leads can now be made with short lengths of flexible wire, and the primary can be removed without having to undo a soldered joint. 3*Tube for Secondary Slot with Primary — Winding • Secondary Winding rrreYvrYTjorrjornGfinQao C. L of form' FIG. 3 The form is wound as usual, the greater part of the wire lying exposed between the arms, and therefore we are justified in calling the coil a low loss one. So far as efficiency is concerned, it will be found that a coil made in this manner compares very favorably with coils made to the standard design. A form of this type is really far more difficult to describe than to make, the one shown in the illustrations being made and wound completely in less than two hours. C. A. OLDROYD, Barrow-in-Furness, England. A RHEOSTAT SUB-PANEL FOR THE ROBERTS RECEIVER A SIMPLE method of eliminating the rheostat knobs from the panel front on the Roberts receiver, is shown in the accompanying Fig. 4. It consists of a sub-panel, SP, about 2 x 4! inches, on which are mounted the FIG. 4 rheostats. On this sub-panel are bolted two small brass angles, one at each end. In order to avoid bolt heads showing on front of the panel p, a small hole should be drilled almost through the panel from behind and tapped for a short bolt. Then the sub-panel is screwed to the panel. If a brace is used for the panel, one of the bolts can be so arranged that it will answer for •ft Tested and approved by RADIO BROADCAST ~ both the brace and angle. It is well to keep the unit high on the panel, allowing just enough room for the rheostat knobs to clear the cabinet easily. This unit will fit perfectly over the antenna and secondary coils in the Roberts receiver. For a slanting panel it is advisable to bend the angles so that the subpanel is parallel to the base board. The unit allows easy adjustment of rheostats, and makes possible the simplification of the panel on any set where the rheostat adjustment, once determined, has little or no effect on the operation of the set. L. D. SAUER, Dayton, Ohio. A SIMPLIFIED BATTERY THROW-OVER SWITCH THE layout in Fig. 5 permits, by a simple twist of the wrist, as it were, the connection of the storage battery to the set or to the charger, as may be desired. The old "clip and plug" process has been discarded, and in its stead a doublepole double-throw switch, with permanent wiring, has been substituted. This hook-up can be used for panel or wall mounting, or may be used inside a radio table or cabinet. This, I believe, to be an improvement over the hook-up contained in the Apri, RADIO BROADCAST inasmuch as a two-blade knife switch is substituted for the threeblade switch; furthermore, the necessity for the extra long contact connecting the charger to the line supply (which type of To Set Power Supply Discharge t t t o3F3 o -0 ^Q 0 Recharge — 1— _110V '' Input — +• Storage Battery an Charger Output 'III. -9 9. I V FIG. 5 throw-over switch must be specially constructed), is eliminated. H. R. NICHOL, Washington, District of Columbia. A PRECAUTION TO PREVENT TUBE BURN-OUTS FIVE perfectly good vacuum tubes had burned out and the owner was afraid to put any more in for fear that they would go too. Here is what the service man found when he came to look at the inst illation. Acid had at one time been spilled on the go-volt cable and had eaten away all of the insulation. This bare wire had apparently bumped up against the negative pole of the storage battery. The negative B lead being connected with the positive of the A battery, the full 90 volts were placed directly across the tube filaments, thus burning them out. The lesson to be learned from this is that one cannot be too careful in keeping the storage battery free from excess acid and also to keep trie wires well separated at all times. If separate compartments cannot be had for the two batteries, it is always best to fasten the various wires with staples so that they cannot possibly be mixed up and cause damage. K. B. HUMPHREY, Brooklyn, New York, j