Radio Broadcast (May 1929-Apr 1930)

THE SERVICEMAN'S CORNER In "The Serviceman's Corner" for May, we considered the simplest and most inexpensive types of radio testers . We publish below a compromise between these more elementary models and the highpriced commercial instruments. The compromise, however, is merely one of price. The outfit described below is as elaborate and efficient as any portable equipment can well be. The contributor is F. W. Howard, radio electrician, of 444 Lakeview Avenue, Pitman, New Jersey. A standard service test set: "The following description of a set and tube-tester constructed by the writer may serve to bring encouragement to some brother serviceman to whom a set-tester and a seat on the Stock Exchange mean the same thing. "The total cost of this outfit need not exceed $25.00, even if every part of it has to be purchased new, and, as a matter of fact, nearly every serviceman will find a good part of the necessary equipment lying around his shop. "Reference to the drawing will give the panel layout of the instruments, the dotted rectangle at the bottom representing the C battery, which is placed upside-down under the panel, and held in position by strips of the brass, which are in turn screwed to the brass frame. "The mounting for the 0.1 meg. resistor is also fastened to the under side of the panel, between the meters and switches, E and F. The writer strapped this mounting between the top screws of the two Weston meters, thus avoiding the necessity of having screw heads showing on the face of the panel, but this is a matter of personal choice. "The connections are shown in the diagram. Here it will be noted that each of the four switches has the direction of its throw indicated by double-pointed arrows, with an asterisk showing the position given on the panel layout. This might be termed the normal position for tests on d.c.-tube sets. "In operation, connection is made between the tester and the socket of the set under test by means of a two-foot cord having tips on one end and a plug on the other. Plugs should be made up for all types of tubes. The writer has three plugs, for x base, y base, and v (standard) base. For testing uv-199 bases, or wd-11 type, use adapters which may be purchased at any parts store. In the case of uv-199, wd-11, and uv-201a tubes, it will also be necessary to use adapters in the sockets on the tester. The writer was unable to purchase one of the latter adapters, so he made one by bolting a standard uv-type socket to the top of a ux-tube base, connecting from prongs to springs with short pieces of wire. This serves to test uv-20lA-type tubes. For testing uv-199 and wn-11 tubes, socket adapters were found which fitted into the iiv socket of the homemade adapter. "It is advisable to use different colors for the wires between plugs and tips, having corresponding wires of each cord of the same color. Thus, a solid blue would be — fil., blue with red tracer +fil., yellow grid, red plate, and for uy base, white cathode. "These cord pins fit into the tip-jacks at the top of the panel, No. 2 being minus fil., No. 3 plus fil., No. 4 grid, No. 5 plate, The Modern Radio and Equipment Company, of Buffalo, N. Y., installed a public-address system at the aviation show in exchange for booth space. and No. 6 cathode. Nos. 1 and 4, with switch F thrown to normal (right) position, permit using the C battery as a source of low voltage d.c. for continuity tests, in connection with an external meter, or the same thing may be done using jacks Nos. 1 and 2, with switches D and E in normal (left) position, whereupon pushing button J gives a reading on the d.c. voltmeter if the external circuit is closed. "It will be noted that switch D is a reversing switch for the d.c. voltmeter, which is very useful in testing certain types of sets, such as Radiola 20 and 25, where every other socket has reversed filament connections. "Switch E shifts voltmeters, which is about the only necessary change between testing a d.c. and an a.c. set. "Switch F cuts the local C battery into the grid circuit, thus making it possible to test a tube for "grid swing" in a socket which normally has no bias. This gridswing test is made by pushing button J with switch G in its normal (right) position, thus connecting the plate circuit through the milliammeter. If it is deemed inadvisable to short the bias in this manner, switch F may be thrown to the center position, opening the grid circuit. "Throwing switch G to the left position makes a high-reading voltmeter out of the milliammeter, with a reading of 100 volts per mA., and an accuracy plenty good enough for most tests. In this test position, button K gives cathode voltage, and button L gives plate voltage. " Inductance switch H is a multiplier for the d.c. voltmeter, giving 2J, 5, and 10 times normal readings. Inductance switch M is a shunt connector for the milliammeter, giving 2, 5, and 10 times normal. The writer wound these shunts by taking a shieldshaped piece of thin fiber which was anchored under the terminal nuts of the Weston meters. This fiber was pierced with several parallel lines of small holes, and the resistance wire passed in and out of these holes. For the multiplier resistance it is advisable to obtain some very small wire, as considerable resistance is necessary. "The writer carries his tester in a cash box which measures 13" X 9|" and is 4" deep. The brass supporting frame is therefore made 3j" high, and the full length of the tester, the "runners" having felt strips shellacked to their under sides, to prevent scratching the customer's furniture. The 9\" width of the box allows room to carry a 201a-, a 226-, a 227-, a 171a-, a v-199-, and an x-199-type tube in a line between front of box and side of tester, which serve to keep the tester from rattling around, and also insures a spare of each of the common types of tubes. "The list of parts, with designations corresponding to those on the plan of the panel and on the circuit diagram, is as follows: A — 0-7 Beede a.c. voltmeter; B — 0-10 Weston d.c. voltmeter; C — 0-10 Weston milliammeter; D and G — Yaxley three-pole, double-throw, center position jack switch; E and F — Yaxley single-pole, double-throw, center position jack switch; H and M — Yaxley four-point inductance switch; J, K, and L — Pearl center push button; S — Eby sub-panel-type four-prong socket; SS — Eby sub-panel-type five-prong socket; 1-6 — Yaxley tip jacks; 7" to 12" hard-rubber panel; 4' of i" x TJ" brass strip; 4i-volt C battery ; 100,000-ohm 2-watt Tobe Veritas resistors and mounting; Resistance wire from old 200-ohm potentiometer or equivalent. Miscellaneous | ome helpful information on Zenith Sets: a Zenith model 1 1-e or 14-E a 16-ep gets so that the volume does not remain steady after a station has been tuned-in, it is very often caused by the rotary plates of the gang condenser becoming loose on the shaft. " I have found a great number of Zeniths with this ailment and I find that a very efficient way of repairing a set of this type Some help/ "When or even 110 O • JUNE. 1 929 •