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Switching device
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Radio set testing apparatus
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Electric meter
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Method and apparatus for testing thermionic tubes
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Method and apparatus for testing audion tube circuits and devices
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Tube testing system
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Set checker
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Meter
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Radio testing device
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Thermionic-valve-testing instrument
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Alternating-current voltammeter
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Radio tube tester
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Radio testing device
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Radio-tube-testing instrument
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Electrical measuring equipment
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Electrical measuring instrument
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Electrolyte-level indicator
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Battery tester
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Radio tube tester
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