In an earlier regionality piece I wrote "the EL34 pushes the mids forward and breaks up early," "the 6L6 has wide headroom and a thick clean." In guitar-amp talk, almost a staple phrase.
But let me honestly ask myself. Is this "the EL34's mids" a fact backed by measurement data? Or received wisdom long handed down? The answer isn't cleanly either. A measurable difference, received wisdom, and confounding (a mixing of causes) coexist within one phrase. This piece is an attempt to honestly separate them. And this separation connects straight to why CSL records not "the type number" but "the state as it rang."
A "measurable difference" in the tube alone certainly exists
First, that the EL34 and 6L6 are different things is clear. This part isn't received wisdom — it's a matter of structure and rating.
The EL34 is a true pentode, plate dissipation about 25W. High sensitivity, starting to distort earlier at a relatively low voltage. Its overdriven harmonics are complex, tending to carry more upper harmonics. The 6L6 (GC) is a beam tube, plate dissipation about 30W. Wide headroom, tight lows, a tenacious clean. Speed of breakup, harmonic distribution of distortion, output impedance (= damping on the speaker) — these actually differ per tube and can be measured.
So "the EL34 and 6L6 sound different" is beyond doubt. The problem is how to word that difference, and how much of that wording you can credit to the tube.
But "mid presence" is hard to show from tube-only data
Here's the crux. Taking out the frequency impression "the mids come forward" as tube-only data is actually quite hard.
To begin with, a power tube doesn't have a fixed "frequency response" like a speaker. The tube's effect on the sound appears indirectly, through behaviors like how it distorts and its output impedance. And much of what you feel as "the EL34's mids" is mixed with non-tube elements. Confounding.
- Circuit (tone stack): Fender-style tone circuits scoop the mids easily; Marshall-style keeps the mids. A mid hill or valley can be made by tone-stack design alone.
- How negative feedback is applied: apply deep feedback and it's tight and quiet; shallow, and the mids and distortion come forward. Even the same tube, the expression changes greatly here.
- Speaker: the so-called "British mids" are also the character of Celestion-style speakers themselves. A good deal of the mids ringing is the cone, not the tube.
So the phrasing "EL34 = mids" usually compares whole Marshall (EL34 + Celestion + shallowish feedback) and Fender (6L6 + Jensen + deeper feedback). The mid difference you hear there is an inseparable mix of the tube's doing, the circuit's doing, and the speaker's doing. Cutting the frequency "mid bump" out as tube-only data is hard because of this confounding.
Yet it's not a complete myth either
So is "the EL34's mids" merely a preconception? Not quite that either.
On the same amp, swap only the tube from EL34 to 6L6 (or 6550) and re-bias. Even comparing under this condition, the tendency "the EL34 is more mid-leaning and aggressive, the 6L6 tighter with more headroom" is reported consistently, with reproducibility, by many people. Since the circuit and speaker are the same, this is the tube's contribution. So it's not entirely made up.
But — the effect isn't as big as the cliché says. The difference the "British vs American" scheme makes it carry doesn't come from the tube alone. The difference a swap on an identical amp produces is smaller, subtler. That it sounds like a big difference is, to repeat, because the tube difference has circuit and speaker differences added on top. The tube's effect is real but overestimated. This is roughly the view of people versed in electrical design too.
So this story is CSL's very subject
Sum up the above in one line: "the EL34 has thick mids" is a composite of a measurable tube difference + large confounding + a somewhat exaggerated received wisdom. There's a factual core, but take it directly as a tube spec and you mistake the source of the sound.
This structure overlaps closely with what CSL keeps writing. In the bias piece I wrote "the tube type alone doesn't decide the sound; the use (circuit) works." In the regionality piece I reserved "the label and the actual sound are separate," "a tendency, not a law." In the spec piece I wrote "a catalog's numbers tell only half of how it actually rang." The type number is a label showing the sound's entrance, not a fixed sound. "The EL34's mids" is a typical example.
Which is exactly why CSL doesn't discuss the sound to the end by type number. Instead of writing "this amp is EL34, so the mids are thick," it records how that unit actually rang — under a certain cab, a certain mic, a certain setting — the state of the output itself, conditions and all. The tube's name is full of confounding and doesn't guarantee the sound reaching the listener's ear. But a record of the state as it rang preserves that sound whole, confounding and all. Instead of trusting the type number, keep the rung result. That's the most practical conclusion drawn from this separation.
In short
Is "the EL34 has thick mids" data or received wisdom? The answer is in between. The tube-alone measurable difference (structure, rating, distortion harmonics, speed of breakup) is real. But the frequency impression "mid presence" is inseparably confounded with circuit (tone stack, feedback) and speaker (Celestion), hard to show as tube-only data. A swap on an identical amp shows a consistent tendency, so it isn't a myth, but the effect isn't as big as the cliché says.
The type number is a convenient label when hunting a sound. But what that label promises is a direction, not the actual sound. Which is exactly why, rather than swallowing the label, keep the state as it rang. This separation around "the EL34's mids" is the example that best reflects what CSL is trying to keep.