EVH 5150III 50w El34 issue or normal?

[adrianher]

Hi there, I’ve got a used EVH 5150 III El34. It arrived this morning. I was testing it and when I use ch1 and 2 (green and blue) which share EQ, the treble knob when I turn it up it decrease volume lvl. If I Crank it all the way up there’s no volume, independently of channel volume knob.

Can anyone tell me if it’s a normal issue, or what could be making the issue? I’m newer on 5150iii amp.

Thanks a lot
Adrian