Mojotone Preamp Tube Taste-Testing
Article by Dave Hunter
You’ll often hear amp nerds talk of tweaking their tube amps to the nth degree by swapping out preamp tubes to tailor gain, frequency response, overall sonic character and other factors. The practice definitely works, and different makes of preamp tubes will all bring varying sonic personalities to the game. The trouble is, it’s difficult to know where to start without relying purely on manufacturers’ hype, or diving in blind to try several tubes for yourself—which can be both pricey and time consuming.
To that end, I’ve put significant playing and listening time in with five of Mojotone’s most popular current-make 12AX7s (some of which also go by their British designation ECC83). The “taste-testing” here should give you some reliable clues on what to expect from each of these relatively affordable tubes in different applications. Note that these assessments were made entirely while playing these tubes “live” in the different guitar-and-amp configurations described and then again while listening back to the several recordings I made of each tube in each configuration (sample MP3s of which are available here), without any reference whatsoever to the manufacturer’s or sellers’ write-ups for each product.
In each of the two test amps used (as described below), the tubes were sampled in the so-called V1 position (for “valve number one”), which has the most significant effect on voicing and tonal characteristics in the preamps of most guitar amps. Keep in mind, also, that the differences between one tube and another might be quite subtle in some instances—and that these variables are further compounded by amp settings—but they are quite real, as revealed in the tests of this selection of 12AX7s.
Guitars, Amps & Settings
Two samples of each tube were recorded using a Les Paul with OX4 Medium-Wind PAF-style humbucking pickups into a Friedman Small Box 50-watt head (a modded-Marshall-style amp with EL34 output tubes) and a 4x12 cab with Greenbacks, using the Plexi channel for “Cleanish” and the Lead channel for “Overdriven”.
For the “Cleanish” clips, playing starts on the bridge pickup, then switches to the neck pickup around the 0:12 to 0:15 mark (depending on the individual clip).
For the “Overdriven” clips, playing starts on the bridge pickup and switches to the neck pickup around the 0:20 mark.
Two further samples of each tube were recorded with a Stratocaster with vintage-wind Rocketfire Total ‘60s single-coil pickups into a Cutthroat Audio Down Brownie brownface Fender 6G3 Deluxe clone with a Weber Alnico speaker. The Normal channel was set for clean for the “Strat Bridge” clips, and both channels were jumpered for a little more gain for the “Strat neck” clips.
Electro-Harmonix 12AX7EHA short-plate 12AX7 with spiral filament to reduce noise, made in Russia.
General Notes: Positives are that it’s a fairly warm, weighty tube; has a little more girth in the lows and lower midrange than some others in this batch, but sacrifices some sparkle and clarity in the upper mids and highs. Can sound a little dull or muted at times when you want a lot of “chime” and detail in clean or driven tones, but you can use that attenuated response to your advantage to tame overly bright or harsh preamps, although it does counter that a bit by breaking up somewhat early.
Overdriven: A little hazy amid the dirt. Decent balance, and feels less hot than the Tung-Sol or some of the others, possibly because it’s less harmonically saturated. It favors the midrange some, but can also sound a touch constricted.
Clean: Pretty well balanced, and can be chimey without being particularly sparkling or detailed in the harmonic overtones. Could be considered “dull” in an amp that needs livening up.
Good For: Taming a harsh or overly bright amp, or adding lower-midrange and low-end girth to an amp that needs to be more weighty. Also might be appropriate in some situations where you desire an earlier onset of preamp clipping.
TAD 12AX7A-C “Premium Selected”A short-plate 12AX7 selected by TAD to meet stringent parameters, made in China.
General Notes: A very “lively” tube both clean and overdriven. An excellent sounding all-around 12AX7, with great clarity, a lot of harmonic sparkle, and a rich, well-balanced tone. Not particularly scooped, but not hyped in the midrange either. A very “high quality” sounding tube overall. Tight lows, without being boomy.
Overdriven: Succulent harmonic overtones and a sweet crispiness amid overdrive, which enhances the sense of articulation. A slight “slurring” of the transients (thanks to abundant harmonic overtones) that is dynamic and fun to play, without sacrificing much clarity.
Clean: Appealing and throaty, with a nice, vocal warmth to it, especially when pushed (or on the Les Paul’s neck pickup, for example). Crisp and chimey on a bridge pickup, without being harsh, and with an enjoyably jangly texture, and just enough compression when hit hard to give it some tactile playing feel.
Good For: A great all-around tube for most purposes, especially when you want to “liven up” the sparkle and chime, and saturation and overtone content, of a potentially muted amp, or just to make the most of an amp that already excels in those departments.
TAD ECC83 WA “Premium Selected”Distinctive short, silver plates and triple-mica construction for low noise, made in China.
General Notes: Warmer and slightly more muted overall than its sibling the TAD 12AX7A, with a little more body in the midrange. This can work when you want to enhance that kind of response from an amp, although the other TAD tube is the choice if you’re looking to maximize sparkle and jangle and chiming harmonic overtones. The ECC83 WA does have a good, rich, vocal quality for leads both clean-ish and overdriven, however, and slightly bigger low end.
Overdriven: Juicy, somewhat darkly saturated, and warm sounding. Good clarity and good balance, and perhaps not a lot of liveliness in the highs, but that’s countered by enhanced midrange punch and pretty significant gain, and a good, thick overall tone when driven.
Clean: Less sweet and less sparkly than its TAD sibling, but full sounding and a little punchier in the mids when clean. Slightly hotter—it breaks up the guitar signal a little easier when you hit it harder at semi-clean amp settings. Low string runs have good girth and presence (on the Strat’s single coil in particular, or the Les Paul’s bridge pickup).
Good For: Enhancing a classy, rich, warm-leaning tone from any amp; taking some fizz and sizzle out of your high-gain tones, adding a girthier low end, or taming overly spiky or harsh clean tones without going dull or muted.
Tung-Sol 12AX7A reproduction of classic short-plate European construction, made in Russia.
General Notes: A musical sounding tube with a very appealing all-around character. Plummy and vowel-like in the midrange without being pushed, and very sweet and balanced overall. An impressive marriage of depth and shimmer in just about everything it does.
Overdriven: Nicely crispy and clear amid overdrive with a sweetly crackly edge to the highs, yet without ever being harsh. Full and rich sounding with good harmonic saturation, and a vocal and expressive midrange that isn’t overly hyped. Rounded but respectable lows. A classy OD tube.
Clean: Tasty brightness and articulation when clean, yet with plenty of depth and fullness. A great balance of body, jangle and chime, while avoiding spikiness even on the Strat’s bridge pickup.
Good For: Enhancing the “quality feel”, clarity, richness, and harmonic spectrum in just about any amp. Should improve articulation in a preamp that currently houses a dark or muddy tube, while likely being a complement to just about any playing style.
Mullard 12AX7A reproduction of the legendary long-plate British Mullard ECC83, made in Russia.
General Notes: Warm, smooth, and rounded, with a silky, elegant feel through most amp settings, but also potentially a little dark or muted if your amp already tends in that direction. Full lows and a good balance throughout the spectrum, while adhering to the above tendencies.
Overdriven: Creamy and rich, yet with very respectable clarity and appealing harmonic overtones when pushed, with a solid but not over-hyped midrange. A slightly recessed attack when driven, couched in nicely touch-sensitive dynamics.
Clean: Warm-leaning when clean, yet with some respectable and velvety-edged chime amid arpeggios or twangy lead lines. Good balance throughout clean to early-crunch settings, and a rich, elegant response to single coils played clean.
Good For: A good tube for helping to tame the harshness in a fizzy or strident preamp, while also adding elegance and depth. Likely an excellent choice if you need to reduce “ice pick” spikes in a clean amp used with single coils, while also able to add creamy thickness to humbuckers for classic-rock tones.