The B & K Precision Model 510B Transistor Tester and Model 520C Semiconductor Tester are designed for in-circuit and out-of-circuit transistor testing, with special features for making additional tests on devices out-of-circuit. Both instruments use both a high-current, low duty-cycle pulse technique to test transistors in the presence of shunting circuitry, and a low-current drive system which enables the user to identify the terminals of the device in most in-circuit tests and all out-of-circuit checks. The instruments are designed for a minimum amount of control manipulation, making for rapid testing of most devices. A 9V alkaline battery is supplied with the instrument and must be connected prior to use. SPECIAL FEATURES Model 510B and Model 520C 1. Patented limited-energy pulse circuit permits highly successful use of in-circuit testing in the presence of low shunt impendances with complete safety for the device under test. 2. A human-engineered panel design which eliminates the need for reference to the operating manual - only three switches, no panel adjustments. 3. Six-position TEST switch sequentially connects the device being tested in all possible configurations, making it unnecessary to know the device terminal identification. Can be left in GOOD position so that additional tests can be made without memorizing test position. 4. Base or gate lead identified by color as TEST switch is operated when testing with HI drive. All leads of transistor are identified when testing with LO drive. 5. Automatic polarity indication to identify NPN or PNP type devices. 6. Clip-on test leads that make positive connections to devices in difficult locations. Free operator’s hands to make further tests. 7. Choice of test leads or front panel socket for out-of-circuit tests. 8. Optional battery or adapter instrument power. 9. Power down mode when operated from 9V battery.