I got 2 questions pertaining to Tube Amps.

1.) How do you tell when your Tubes (power and pre) need replacing ?

2.) I'm having trouble dialing in my tone with my new tube amp, this is my first tube amp so I'm not too knowledgeable in EQing them. I play Death/Hardcore Metal and use a Peavey 5150 through a Bheringer Cab. Basically i was hoping someone could give me some advice on EQing my head and getting the tone i'm looking for.
Agile Septor Elite 7-String
ESP H-1007
ESP H-1001
Peavey 5150
Mesa Boogie Cab

Recording Gear -
PreSonus FireStudio Interface
CX5 Studio Monitors
well im not sure of the technical term of knowing when to replace the tubes but i think its just when it really gives a **** tone.

To EQ ur amp put ur gain high and ur bass as well, if u want a more steely sound but up the treble. but basically u are looking for more of the heavy sound so the bass and gain should be accordingly high. the middle or high should be half way or less (depending on the sound u want)