AND I almost forgot, depending on the style of tone bleed on the guitar different length cables really seem to work for different guitars. My SG without a treble bleed sounds best with a 10 - 15 ft cable while my prs with a standard 200pf-ish treble bleed on it sounds best with about 40 ft of cable between the guitar and the amp. Really guitar dependent for cable length though probably as much as treble bleed, definitely worth trying different combinations.

I'm reviving an old thread in the hopes that someone might benefit from my trial and error.

 I tried a TON of different combinations of tubes in my Expression and by far the best I've found are V1: either NOS RFT or new production Tung Sol 12ax7 V2: JJecc83s V3: Sovtek12ax7LPS, preamp tubes are important for sure, but the biggest tonal differences I found with trying different EL34s.

 I tried Winged Cs( not bad, but shrill and honky), EHX 6CA7( thin, shrill, and honky), new production Mullard( AWFUL), JJ EL34( ok, but honky), JJ E34L ( a little sluggish and honky), and a few more almost all of them made the amp sound harsh or harsh and honky.

 By far the best I've found are the Shuguang EL34B, sold as Sino EL34B via Tubedepot. Smooth, no harshness, no honkiness. Sounds like a nicely balanced EL34.

A couple other things to note: The PPIMV is almost useless and only sounds good at 3 o'clock or above and sounds best turned all the way up. I found the parallel ceramic and poly caps between V1 makes things too mushy on the low end, especially for humbuckers and even more especially for higher output humbuckers so I removed the .002 ceramic cap. I went from having the bass dialed all the way off to being able to use it between 9 o'clock and noon without any flub or mud. If I used the PPIMV I'd probably not remove the cap however as things get thin quickly once PPIMV is turned down.