Check the listing for details. Bias Tool testing probe for tube amp amplifier biasing adjustment MADE IN USA. Condition: New. Listed at 24.75 USD. Proudly made in the USA! No offshore junk here- these things will last... You are looking at a top quality original SRS BiasTool, new, sealed, instruction sheet included. Used world-wide by tube amplifier technicians for correct measuring of bias, a critical measurement and adjustment required when installing new output tubes in a tube amplifier. Works with 5881, 6550, 7027, 8417, 6V6, 6L6, 6CA7, EL34, KT66, KT77, KT88, KT90, and many more- if you are unsure, or do not see your tube type listed here, please contact us prior to purchase to verify if this device works with your tubes and/or amplifier, and we will gladly help you out. This listing is for one(1) SRS BiasTool only, brand new. The meters and amplifiers in the pictures are not included.