Grove Tubes is really just a distributor of tubes. Other companies make tubes for them, and Grove Tubes put their name on the ones that meet their standards. So I'm afraid that doesn't tell me much either.
Take a look at the tube and see if you can find what model of EL-34 they are.
Oh, by the way, did you check to see what kind of cable you're using to hook up your head and cab? You should be using a short fat speaker cable. If you're using an instrument cable turn your amp off immediately! This could break your amp!
Another thing, tubes can be finnicky. It's not all that unusual to get a new one that doesn't work right.
I highly doubt a rebias is going to solve your problem. To me it sounds a bad preamp tube. If you can post a video clip of what your amp is doing that would help.
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