Radio broadcast .. (1922-30)

Data on Its Construction and Use AN EFFICIENT RADIO SET DIAGNOSER By HERBERT M. ISAACSON Engineering Department, Colonial Radio Corporation T! well n BENEFITS to be derived from the use of a set-tester or "diagnoser" have been so rehearsed that they are fa- miliar to every serviceman. A diagnoser facilitates rapid, sys- tematic, and accurate testing of a receiver, since any deviation from the normal in either set or tubes gives a visual indication on the panel of the tester. Because each circuit of the receiver is checked individually, the faulty circuit is isolated quickly, and the trouble is run down to the defective piece of apparatus. To a large extent, then, it removes the guess work from servicing and enables the ser- viceman to make an accurate diagnosis of the fault in a minimum of time. Important Features The diagnoser described in this article embodies all of the features found in the best of manufactured test sets, and, in addition, it has several points of superiority which have been developed by the writer. The important features of the diagnoser are as follows: 1. .Portability: The tester measures only 8 X 11 X 4 inches and weighs seven pounds. 2. Ease of manipulation: All read- ings are obtained by depressing push buttons. These buttons may be locked in a closed posi- tion when desired. 3. Universality: The tester is capa- ble of checking any standard receiver or tube without requiring the connection of extra leads or external sources of power. (See Fig. 1.) 4. Completeness: The tester tells a com- plete story. It. will measure filament, grid, plate, and screen-grid voltages and plate currents existing at the tube sockets of the set. Complete circuit continuity may be checked, with one exception—the grid circuit of a grid leak-condenser detector. RAulO otl UlAbNUotK HERBERT H. ISAACSON QRV RADIO SERVICE.INC, MILUtMFERES SOO 10 100 1000 ' VOLTS OC View of the diagnoser designed by the writer. Adaptability: The various current and voltage ranges of the meters are avail- able for external connection and the tester is designed so that special tests may be performed easily. For example, heater and line voltages may be meas- ured and the polarity and charging rate of trickle chargers may be determined. . Serviceability: Simplicity of design in the mechanical features and the selection of quality materials in the construction insure serviceability. 7. Foolproof: Any or all of the buttons may be locked down simultaneously without damage to the diagnoser or the set un- der test. 8. Versatility: By use of the diag- noser, sets can be neutralized, overall sensitivity checked, ef- fectiveness of pick-up systems tested, degree of shielding of loop-operated sets located in steel buildings investigated, po- sition of break in concealed in- door antennas found, capacities of condensers and the value of resistors in megohms measured, and, in addition, the diagnoser incorporates a feature which has proved of great value—a modu- lated oscillator. The Switching Mechanism Since the diagnoser is built around the switching mechanism, this unit will be described first. As will be realized from a consid- eration of Fig. 2, the switching assembly may be made of ordinary knife switches. However, a cheaper and better method from all stand- points is to construct a push- button-operated switching mech- anism. Such an assembly with all the switches necessary for the set-tester herein described can be built easily to take a space only 6 inches long, 2 inches wide, and less than 1 inch deep. A compact and symmetrical appearing piece of apparatus is the result. The switch lever C is bent so that it exerts pressure against contact A. When the push button is pressed the contact at A is broken before contact can be made with point B. The circuit connections, of course, are made to contacts A and B and to the switch lever C. With contact A omitted we have a single-pole single-throw switch. By mounting two switches so that the one push button presses both levers at the same time a double-pole double-throw switch is obtained, with levers CC' always Average Values of Plate Current Change for Standard Tube Types *Indicated C bias on Diagnoser is greater than applied by an amount equal to one half of filament voltage if d.c. is used on lilament. Indicated and applied voltages are the same if a.c. is used. 52 • NOVEMBER 1929