Sounds like a bad tube to me. Your vendor should give you a new one.
14 responses Add your response
In case ghdprentice has gone to bed, if your tubes were bought as a match pair your vendor should be able to match the tube he sold to you. Each tube (or the box in which it came) should have the tested #. But, even if he can't/won't give you a matching tube, setting an identical bias should get you most of the way. Thing about a match pair is that in use the tubes won't remain matched forever any way, ergo the need to check your tubes bias regularly depending on hours of use.
tritube, You did it correctly, biasing the tube to 40ma as recommended by the manufacturer. You would have done that with any voltage designation on the tube/box. Tubes can be too 'hot' or too 'cold' and be unable to meet the biasing requirement but this rarely occurs. That has happened to me a couple of times with tubes 'tested' at the factory. You should be OK.