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valuable kinks have been written especially for Popular Mechanics Magazine by prominent radio experts. They represent not merely ideas, but practical advice from the best technicians in the profession on methods that will help make your set more efficient in operation, more convenient to handle or easier to build.

 



Here is a simple timesaver any radio owner can make at little or no cost which is especially useful to those set owners who have their batteries installed in a console or radio table-type cabinet where it is difficult to get at them to take a voltmeter reading. To make such a reading is required once in a while to determine the condition of the batteries and, in most cases, it is necessary to drag the cabinet away from the wall and reach into a crowded battery compartment, with the possibility of pulling a wire loose or short-circuiting something. I have eliminated all of this trouble with my set by drilling a few $1/8$-in. holes in the side panel of the radio table close to the top and about 1 in. apart into these holes I bolted some old nickelplated switch points taken from my scrap box. To these I fastened flexible leads inside the cabinet, connecting them to each battery in turn, as shown, so that by putting my voltmeter across any two points I can determine their condition.—H. G. Nebe, chief engineer. Station WSMB, New Orleans, La.

 



With the popularity of the 171-type of power tube, I think the readers of Popular Mechanics magazine might be interested in knowing how easy it is to make an output impedance to keep the B-battery d.c. from passing through the windings of the loud speaker. Not until I had burned one one such winding did I wake up to the fact that something should be done. For the audio choke I used most anything that passed enough current and still offered a fairly high impedance. I am now using 