Check the listing for details. Tektronix 5A21N Differential Amplifier Instruction Manual 1977. Condition: Used. Listed at 19.99 USD. The Tektronix 5A21N Differential Amplifier Instruction Manual from 1977 is a valuable resource for users of this specific product. Produced by Tektronix, a reputable brand in the test, measurement, and inspection equipment industry, this manual provides detailed instructions and information for operating and maintaining the Differential Amplifier. With clear and informative content, this manual is essential for those looking to properly use and troubleshoot the Tektronix 5A21N Differential Amplifier in a professional setting.