Vacuum-Tube Tester
   “Vacuum Tube Testing Outfit, Cenco “Visigram” (Patent No. 1.968,039), designed to aid the elementary student in the usually confusing study of a radio vacuum tube characteristics. Consists of a compact assembly of tube socket, filament rheostat, potentiometer, reversing switch and binding posts mounted on a panel 16 cm square supported about 6 cm above the top of the table. The wire connections are beneath the panel, and are open so that every detail may be examined by the student. The instructive feature, making the unit such an invaluable piece of elementary laboratory apparatus, is the detailed wiring diagram which is worked in with the controls on the panel. At a glance the student can see what potential is on the grid, how it may be reversed, whether all of the filament rheostat is in or out, etc.  The apparatus is designed for use with three electrode four-prong tubes. The high resistance potentiometer, in connection with the reversing switch, makes it 
possible to apply any desired potential to the grid of the tube. Binding posts, neatly positioned around three sides of the panel, provide for the following: -- grid battery, grid voltmeter, filament battery, filament connector, plate battery, plate voltmeter and plate milliammeter. Complete as described, but without accessory measuring instruments … $14.50”    From the 1936 catalogue of the Central Scientific Company.

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