Useful Hints

Radio Record, Volume III, Issue 48, 13 June 1930, Page 31

Useful Hints

N converting out-of-date sets to use modern power valves, it may be found that the eliminator only delivers 185 volts. This is not sufficient for most power valves. Consequently, if one does not wish to purchase’ a new eliminator, a 45-volt B battery must be inserted in series with the B eliminator to secure 180 volts on the plate. The B power tap on the eliminator is taken to the negative terminal of the battery, the latter’s positive terminal thus becoming the positive terminal of the power supply. Of course it will be necessary to renew this added battery from time to time. % * % POWERFUL local station signals will come in on almost any type of aerial, but it takes a really efficient aerial and earth to bring in DX (longdistance) signals properly. * * * ANY amateurs may have a couple of. low-voltage B eliminators, and yet ean they be in difficulties to secure a high-voltage supply. Such a supply can be easily made by placing two B eliminators in series, the total voltage being the sum of the separate units. In this case the positive terminal of one B eliminator goes to the negative of the next. The high voltage is then taken from the two extremities. In a similar manner a dry battery can be hooked up with an eliminator to increase the voltage. . % % . T is a. good plan never to mount spring switches, potentiometers, or rheostats with spring adjustments until the constructor has made sure that the tension on these is sufficient to afford good, strong, positive contact.

I’ some circuits the experimenter may find that there is not sufficient filament current for the operation of 227 valves. To overcome this difficulty, an extra filament transformer may be placed in parallel with the first to give greater current. However, in performing this operation, use a small 3-volt torch bulb across the output of the two transformers when paralleled. If the lamp lights when both the 230-volt line plugs are connected, the secondaries are correctly hooked up. If:the lamp does not light, one of the plugs will have to be reversed. When proper polarity is found, the two single supply lines should be wired together permanently. Ed BS * OT only does the provision of @ suitable grid bias improve quality, but it effects great economy in the B voltage consumption. * aE Ba RACKELING or fluttering in a radio set has been known to be caused by a loose plug in the wall receptacle. If this is the cuse it mny be remedied by putting a slight outward bend on one prong of the plug with a pair of pliers. However, in doing this be sure that too much pressure is not exerte:l on the prong or else the prong will be torn loose from its mooring in the compound from which the plug is made. M" * * VERY aerial possesses a certain amount of inductance and of capacity apart from the coils and condensers associated with it. s x * [* the absence of a polarity plug the radio enthusiast may make a very simple substitute which can be used either on a dc. or a.c, line, If it is found an a.c. set hum 4a little more when the p!:': is in one direction it may be reversed und the hum reduced. After finding the proper polarity, a dash of white paint may be put on the plug ot the pole desired, and another dot of white paint placed on the wall receptacle in which the plug is to be inserted. The two paint marks should meet, thus indicating the plug is in the right direction. . . .