(For those of you who are new, here's why you spell it "amph.")

Anyway, I'm in the process of getting my Jet City JCA22H retubed. I called a tech in Green Bay about getting JJ EL84s put in and biased. That will happen sometime next week. After that, I'm going to turn my attention to the preamp tubes. A couple of general questions:

My amph has five preamp tubes: V1 is the primary gain stage for both channels, V2 is a secondary gain stage for the overdrive/SLO channel, V3 is half for a gain stage for both channels while the other half is a cathode follower, V4 is for the effects loop, and V5 is the phase inverter.

I assume the biggest tone differences would come from V1 and V2. Is that accurate? I had all JJs in my old JCA20H and was quite happy with that. JJs are a bit darker which actually works quite well with this amph which tends to be pretty bright.

Does it really matter what I put in V4? It would seem as long as it's a functioning 12AX7/ECC83 it really wouldn't contribute much to the tone of the amph. Or am I way off on that?

Does a balanced phase inverter really matter? All the tube sales sites seem to think so, but just about everything else I've read indicates it's not worth the upcharge, at least in a guitar amph.

V1 and V2 have tube covers on them. Are they really necessary? Do they just unscrew or is there something else you need to do.

Inquiring minds want to know!