Thank you guys for all the feedback. It has EL34's in it now.
I was looking for something that wouldn't make the tone not so "soft".
I like a fast pick attack and a stiffer feel. I'm wondering if the Herbert is for me? : /
EL34: crunchy, aggressive mid-voicing. Marshall-like tone & feel. Adds some compression, not as tight bottom end.
KT77: more modern sound, adds more high-end, and definitely more bottom, slightly mid-scooped, less compressed.
KT88: really open, least compressed tube around, not a very smooth breakup, super tight bottom, clear, articulate, tight... emphasis on high and low end. Bright, clear, chimey cleans.
6550: open, crunchy, like a combo of EL34 & KT88 (closer to the KT88)... smoother/sweeter distorted sound compared to KT88s... really tight bottom end, with added low-end chunk. Not as good clean tones as a KT88.
6L6GC: mid-scooped, nice high-end... not as tight in the lows as KT88/6550... but better than EL34 and more open sounding and less compressed. Best for cleans and mild crunch.
I've tried all of them. I like KT77s & EL34s best. 6550s are cool too.
Try KT88s or 6550s. These are the tightest most articulate sounding. Caution: These are not recommended by Diezel, so do so at your own risk. They work, but can get hot.
Also, check out a VH4. It's the tightest, most articulate sounding Diezel... but does so with the help of some compression on channels 3/4.