They didn't need to know the mutual conductance or transconductance of a tube to fix radios or TVs.
Tubedigger 5.58 tv#
Most radio and TV repair shops did not spend the additional money for mutual conductance testers. Things like analog computers, avionics, servo systems, and test equipment could malfunction if the amplification of the tubes was not within specified ranges. They were mostly used in industrial and commercial settings where a "good/bad" test was insufficient. Since the circuitry is somewhat more complicated, and a lot more work had to go into producing the tube charts, mutual conductance testers were more expensive than the other types.
The tube actually has to amplify in order to obtain a reading, so you can be pretty sure it will meet the desired specification in a radio. This yields a numerical value that can be compared to other tubes of the same type, at least on the same kind of tube tester. Mutual conductance testers go one step further and measure the change in current in the plate circuit caused by a changing voltage in the grid circuit. Consequently, these testers will catch nearly all problem tubes. These test tubes for emission, but the grid elements are connected to a source of voltage different than the plate, so the tube actually has to function to a certain extent before the meter indicates "good." Shorts and gas or leakage are also tested for. It was once estimated that worn-out cathodes were the cause of about 90% of all tube failures, so an emissions tester is good for "culling" the majority of bad tubes that are out there.īetter tube testers were known as dynamic or electrodynamic types. The better ones also test for leakage or gas in the tube. The tube is connected as a diode with all grids shorted to the plate, and the current it passes is measured on a milliameter. Low end tube testers measured cathode emission and shorts. Checking filaments can be done with any kind of meter that tests continuity-no special tester required.
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