When Shifting Valves

Radio Record, Volume III, Issue 48, 13 June 1930, Page 4

When Shifting Valves

MAY set-owners thoughtlessly re move valves from their sockets jn ae. operated receivers without first turning off the ~power switch. This is a very dangerous prac-tice,-as it will generally cause excessive filament (or heater) voltage to be applied to the remaining valves in the set. This unbalancing of filament voltage is brought about by the inherent characteristics of the transforme. winding which supplies power to the filaments. This winding is designed to deliver a definite voltage across the filament terminals when'a certain current is drawn, from it, If the current is increased, the voltage delivered by the winding will decrease; but, if the current is decreased, the voltage will increase. , ‘ From these facts it is easy to see. that the removal of a. valve from its socket ‘when the radio set is in operation will cause a decrease in the current drawn from the filament winding and will result in a corresponding increase in filament voltage. This increased voltage is impressed directly across the filaments of other valves in the set and is instrumental in causing early valve failures.