Tips and Jottings

Radio Record, Volume II, Issue 20, 30 November 1928, Page 28

Tips and Jottings

Concerning Grid Leak. \NHE radio enthusiast may well be pardoned for assuming that there is a law or edict compelling him to employ a 2 megohm grid leak for his detector. As a consequence, much detector efficiency is sacrificed, particularly on DX or the reception of weak signals, Nothing helps reception of very loud signals as well as very weak Signals so much as the proper grid leuk value, even if 2 megohms is a fair compromise, A resistance value of from several hundted ohms to many

Inillion ohms is required, as well as a precise adjustment and silent opera} tion. ; Trickle Charges Voltage. "THE voltage of a trickle charger-or -of any charger, for that matteris not important so long as it is higher ‘than the voltage of the battery charged. Otherwise, of course, ‘the battery would disci arge itself ‘back through the charger. To charge @ sixvolt battery about 10 volts at least are needed; but .within reason, it may be any voltage above this without danger. The charging rate, of course; is more critical, and should be adjusted to suit the capacities of different batteries.. A small 10 ampere battery, for example, should not be charged at more than 1.amp., while 100 amp. accumulators require a charging rate of about 10 amperes. Watch Aerial Joints. QGCRATCHING sounds heard in the midst of .radio reception. during 8 storm should not always be attributed to static. Where the lead-in consists of more than oné piece of wire, the joints should be periodically examined for mechanical and electrical weakness, and places where the lead-in is fastened to the antenna must not be .overlooked, for when the wirés are strained and ‘vibrated in a heavy wind noises will be heard if the joints are not firm. Grid Bias with Push-Pull. A CORRESPONDENT is apparently puzzled at having to use such abnormally high -grid bias voltages in push-pull. He has stumbled on a fact that is puzzling many amateurs, When using two valves in push-pull arrange-. nents, it is possible to bias the valvés to the centre of the bend at the bottom portion of their characteristic curve. The technical explanation is very ‘involved, but by doing so, an enormous output is obtainable, with no distortion. This point is rather critical, and should be adjusted with care. One advantage to be gained by this method is a large reduction of B battery consumption. a 2 ok o