This Triplett 2590 vintage transistor tester is the means to verify and match germanium transistors for repairing those early transistor radios. Germanium replacement transistors are more difficult the come by these days and salvaging transistors from junked radios is a good way to obtain good replacements. But without testing replacements you are going by chance a transistor will perform adequately. Pictured is a 2N3904 transistor under test and is indicating typical Beta (current gain) of well over 100. The tester also tests both transistors and diodes for conductance and leakage. The tester is 120 VAC powered so there's no worry batteries will leak while the tester is sitting unused. The manual explains each test in detail.