Useful Hints

Radio Record, Volume III, Issue 20, 29 November 1929, Page 29

Useful Hints

OOD quality cannot be obtained from a loudspeaker unless a suflie ciently high supply of "B" battery volte age is used. The ideal at which to aim is to supply the maximum jer missible voltage to the plate of the power valve in use. It should be noticed that an extra 10 or 20 volts will be necessary when connecting up to the "B"+ terminal of the last valve, _because a voltage drop invariably takes place across the loudspeaker or the output filter. PROBABLY the greatest difficulty to overcome when working on the very high frequencies is the presence of hand-capacity effects. especially on ,the earthed portions of the circuit such ‘as the filament wiring and the spindle of the tuning condenser. In such Cire cumstances relief can vevally he: 0. tained by disconnecting the earth alto gether, or using instead a few yards of wire on the floor as a counterpoise. Another. expedient which often works is to connect the earth merely to the bottom of the primary coil, and to remove the usual connection with that point to the filament circuit. We then have the usual circuit from the aerial down through the primary coil to earth but the rest of the set is unearthed.