Show Must Use Care to Keep Vacuum Tubes in Order To prolong the life lICe of vacuum tubes the they should be burned as dimly as possible at all aU times Excessive fila fila- filament filament ment current and ond plate voltage have the property of ot destro destroying Ing the coating of thorium on the filament If the ope ope- operator operator operator finds that the tube tuba has to be burned brightly and the plate voltage must be over 00 JO for or good volume the tube should be taken back to the place where it was purchased and a test made Should one find that it Is im- im impossible Im Impossible possible to guess at the proper bril bril- brilliancy brilliancy a voltmeter should be added to the set |