For Gm, 26 is the suggested 60% reject value. For reference we use a calibrated Military TV-7 Tester. The item "5670 (2C51) RCA NOS NIB Audio Receiver Pre-Amplifier Vacuum Tubes Tested Pair" is in sale since Monday, December 27, 2021.This item is in the category "Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Parts & Accessories\Vintage Tubes & Tube Sockets". The seller is "chukv" and is located in Westwood, Massachusetts. This item can be shipped worldwide.