TIPS AND JOTTINGS

Radio Record, Volume I, Issue 34, 9 March 1928, Page 12

TIPS AND JOTTINGS

(By

Megohm

A CORRECTION. In a recent article on two-valve amplifier a misprint caused ‘2 inches" to appear as the diameter of the tuning-coil for the crystal. Further down the samte page, howe ever, the correct diameter, 3 inches, was mentioned. B ELIMINATOR SUCCESSES. YINCE publishing the success of a 9 Christchurch constructor of the "Record" B eliminator, we hear of several others that have been running satisfactorily for some time. Naturally inany eenstructors will not think of sending in a report of their success, but the writer is just as pleased to hear of such as he is to help any constructor who is «onfronted by a difliculty. GLOW:TUBE EXTRAVAGANCE. (PHE use of a ‘glow tube" regulator in B climinators sometimes iniproves the stability of the R.I’. circuit, and reduces the tendency to "motor-boating" and oscillation on the audio side, but unless the eliminator will give an extra 30 milliamps without too much of a drop in voltage, the ‘glow tube" should not be used. Such regulation is therefore only attained at the expense of a heavy drain on the eliminator output.

A CARTRIDGE CHARGER WARNING LISTENERS who have employed a bulb rectifier battery charger always connected to the battery so that switching on the current to the charger would set the battery charging, must remember that if they change over to a Raytheon A charger, they must provide a switch to open the charger circuit. The cartridge rectifier may allow @ drain of as much as 180 milliamps to pass if left connected to the battery when not charging, and this leakage will run down an A.battery in two or three days. A d.p.d.t. switch to throw over for set or charger is the best arrangement. THE LOUDSPEAKER POSITION. (COMMENTING ou the excellence of | the few loudspeakers, and the ‘need for improvement in the many, "Radio Broadcast" says: "It is our opinion that improving the loudspeaker will spell trouble for the designers, manufacturers, and owners of ac. sets. With a Balsa (wood diaphragm) loudspeaker which we operate with a Western Iilectric 540-AW unit out of a single 171 tube with about 160 volts on the plate, the average a.c. set is too noisy for pleasure, although on other loud speakers the hum is inaudible. In other words, the a.c. tube either marks the limit of loudspeaker development, of the newer and better loudspeakers will force a.c. tubes to deliver signals ‘unruffled by ac. hum. We hope the latter, for the average loudspeaker of to-day is less than 5 per cent. efficient, considering the entire audio band to be passed." ,