EXPERTS SAY

Sun (Auckland), Volume III, Issue 759, 4 September 1929, Page 16

EXPERTS SAY

The old-fashioned plan of connecting a by-pass condenser across the telephones is now coming into a limited degree of favour again, as it is often an advantage in short-wave sets. Very often a humming noise can he partly overcome by using a different earth —e.g., if you are using a water main, transfer to a buried plate. Theoretically, the split-primary method of H.F. coupling should produce a greater signal voltage per stage than the split-secondary method, because with the former the full secondary voltage is applied between the grid and filament of the succeeding valve. * ! The commonest cause of low- ] frequency howling is a run-down H.T. I battery. * * * j When a dry battery begins to get | old its resistance increases rapidly, I and its voltage fails. Both of these | factors (particularly the former) tend | to give rise to distortion. Should it be necessary to disconnect all the battery leads from a set, disS connect their ends from the batteries j before taking them off the terminals l on the set. Only low-impedance valves which i can handle a considerable current are ; of use for the output valves. A high magnification factor for a valve is nearly always associated w high impedance, and a low magnification factor with low impedance. The magnification factor of a valve is a figure based on the fact that a few volts on its grid are equal in effect to a larger number of volts upon the plate. | If a valve has a magnification fac- | tor of, say 25, this means that 1 volt i upon the grid will have the same ! effect as 25 volts upon the plate (and i 3 volts upon the grid equal 75 volts I upon the plate, etc.).