A reading of 1300 is the minimum recommended. These GE 6L6GC tubes are from 1960's and 1970's USA production. The 6L6GC is a beam power amplifier tube with octal basing.
It was designed to deliver high power sensitivity with a low percentage of harmonic distortion. This item is in the category "Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Parts & Accessories\Vintage Tubes & Tube Sockets". The seller is "tubes42" and is located in this country: US. This item can be shipped to United States.