In this post, I will be comparing several different brands and models of preamp tubes commonly used in guitar amps, specifically in the V1 or input stage position. The differences between tubes are still noticeable in other stages, but will not be as pronounced as in the input stage, which is why I focused on this position. My reference amp used for this comparison is a Fryette Ultra Lead, which excels in high gain and clean sounds alike, and has a pretty neutral (not overly bright, dark, or abrasive) character that responds well to tube changes, different guitar pickups, control settings, etc.
First up is the JJ 12AX7. While it’s a fairly high gain tube, I find it actually works best in an amp that will primarily be used for clean or lightly driven tones since it has a very smooth high end that can become undefined and muddy under high gain if the chosen amp isn’t inherently bright. This can usually be compensated for with different settings on the amp itself, though, and the JJ also offers a very thick midrange cut.
Next, the Electro-Harmonix 12AX7. This is my favorite tube overall for an input stage since it has a similarly thick midrange response to the JJ, but is a brighter sounding tube overall and retains clarity even with extreme gain settings. This wouldn’t be my first choice for a strictly clean amp, but it works well enough in a versatile amp that has to cover high gain and clean sounds alike. The EHX is currently what I have in V1 of my Ultra Lead.
The last 12AX7 is the Tung-Sol reissue. This tube is clear and defined like the EHX, but is overall more aggressive and hi-fi in that it emphasizes the low end response and top end detail, but leaves the midrange response fairly smooth and neutral. I like to use this tube in high gain amps that are inherently darker in character, but it can be a nice change of pace in other amps when more aggression is needed.
The last two tubes are also from JJ, but the models are the 5751 and 12AT7. These are both direct replacements for 12AX7 positions, but have about 20% and 25% less gain than a given 12AX7, respectively. This is great for amps that will be primarily be used for clean playing or for amps like a 5150 or Uberschall that may need something to slightly reduce their overall gain to increase the useable range of gain. I like the 5751 for its clarity and midrange focus, which is more centered on the higher mids rather than the lower mids like the JJ or EHX 12AX7 models. The 12AT7 takes those traits and adds extra high end detail, which is nice for glassy cleans, but can become brittle and harsh under high gain.