Protecting A.C. Valve Filaments.

Radio Record, Volume II, Issue 13, 12 October 1928, Page 26

Protecting A.C. Valve Filaments.

O protect A.C. valve filaments from mains overloading, especially where the main voltage is habitually higher than the manufacturer's recommendation, « fixed resistance to reduce the mains voltage to the correct value should be placed in series with one of the mains leads. Where the voltage of the mains is variable, a power vheostat of high value may form a handy resistance, as it can be altered to keep primary voltage constant in the receiver. An accurate A.C. voltmeter must be used to measure the mains voltage, but the troxbie of proper adjustment is well repaid by the Saving of valves from being burnt out. Burnt-out Tube as Neutyraliser. AN American journal states that a burnt-out valve may be used\for a neutralising condenser in many /r.f. circuits where the neutralising capacity must be approximately the same as the grid-plate capacity of the r.f. valve. No connection is made to thie" filament legs. The valve must be of the same kind as the r.f. valve to be neutralised.