Why V1 Matters
CONTROL GAIN FIRST
Start with Gain to dial in feel and build genre.
Gain is simply how loud a tube “magnifies”, or better yet- amplifies, the audio signal. The 12AX7 is special because it has the highest gain of 100. Where the 12AT7’s gain is 60 and the 12AU7 only 20.
For example replacing V1 from a 12AX7 to a 12AU7 will reduce the gain significantly, adding headroom, making it much harder for the guitar signal to “clip” aka breakup. In other words, if you are playing metal- stick with a 12AX7. However, if you are playing Jazz or alternative rock, it could be beneficial to explore your amps full range of tone by swapping V1 for something that will give you more headroom.
Gain by tube type:
12AX7 — ~100 gain: breaks up early, lively sound
5751 — ~70 gain: a notch cleaner and rounder, still punchy.
12AT7 — ~60 gain: more headroom, clean feel.
12AU7 — ~20 gain: very clean, late breakup, tame tone.
Pick by goal: more clean headroom → try 12AT7 or 12AU7 in V1; more grit/drive → stick with 12AX7 and change power tubes (part 2).
Tube amps are called tube amps for a reason: tubes aren’t decorations—they’re literally why your guitar sounds amazing.
Your guitar is weak. Not in terms of swagger, but in terms of signal strength, it makes a tiny signal. Historically, this weak signal could only be boosted to audible volume by well… tubes.
When your (weak) guitar signal hits the V1, the first tube in your amp, it amplifies your guitar signal and passes it downstream to the next tube. Because V1, by definition is the first tube in line, small changes made here get magnified through each stage before they hit the speaker. This is why rolling this tube can make one of the biggest differences in how your amp feels and sounds.
THEN EXPLORE PLATE TYPE
Once the gain feels right, fine-tune character with preamp tube era and plate style.
Long-plate 12AX7s tend to sound warm, wide, and a little “bloomy.” Black long-plates lean even warmer and read as more “vintage.” Short-plate versions — like RCA 12AX7A or Mullard 12AX7 — trade a touch of warmth for tighter focus and extra detail.
For more information check out our other articles in our Tube Buyer’s Guide like the Best Tubes for Fender or Marshall amps or our Plate Cheat Sheet.
In general, vintage tubes sound warmer, more natural, and less harsh; modern tubes can lean brighter or brittle, so we don’t suggest rolling modern tubes for this guide.
Part 1 Wrap-Up — Start at V1
The simplest way to roll tubes without getting lost is to start at V1 and choose your gain first. If you want more drive and earlier breakup, stick with a 12AX7. If you want to tame things a touch, a 5751 nudges the gain down. For cleaner headroom and a more open feel, a 12AT7 does the trick, and a 12AU7 is the calmest of the bunch.
Once the amount of gain feels right under your fingers, then chase flavor. Long-plate 12AX7s tend to sound warm and bloomy, black long-plates lean warmest and “vintage,” and short-plates (think RCA 12AX7A or Mullard 12AX7) trade a little warmth for tighter focus and detail.
Make changes one at a time and keep the variables consistent. Play the same riff at the same volume and take a quick note about what you hear—how soon the amp breaks up, whether the feel is squishy or open, if the highs are smooth or edgy, whether the lows feel loose or tight, and how quiet the background is. Two or three swaps like this will tell you more than any spec sheet.
A quick safety reminder before you start swapping: power the amp off, let it cool fully, pull tubes straight out (don’t wiggle), and be sure the replacement has the same pin count and type. If something feels tight, stop and realign the pins rather than forcing it.
In Part 2, we’ll follow the signal downstream to the other preamp stages and the power tubes—and how those choices shape gain, noise, and overall feel.