There are so many different amplifier tubes out there that the nuanced differences between them often get lost. Generally speaking, it’s as simple as using EL34s for a "British” tone and 6L6s for an "American” tone...right?
According to Mark Bartel, mastermind behind Tone King Amplification, it's not that simple. Rather, it’s paramount to consider a number of other factors when making your decision.
"I consider the 'power section' as including both the output tubes and the phase inverter since a lot of the behavior happening here is a result of the interaction between these two components,” says Bartel.
"To me, the most important contribution of the output stage is the dynamic response of the amp. A designer can manipulate the circuitry of the output stage to make it feel stiff and fast, or soft and loose, or anything in between.”
What this means, according to Bartel, is that you cannot simply throw a set of EL34s into a Fender Deluxe Reverb and expect it to sound or feel like a Marshall Plexi or JCM 800. However, Bartel noted that an amplifier's output stage – and specifically its power tubes – have a dramatic effect on the harmonic content it lends to the sound. This is especially true when pushed to overdrive.
"Each tube type has its own harmonic profile that works together with the voicing of the amp's circuitry to create the basic sonic character of the amp.” Bartel also added that different tubes have vastly different characteristics best suited for some players but not all.
6L6 vs. EL34 Tubes
How about the difference between that classic, glassy "American” clean sound associated with the 6L6 tube and its raunchier counterpart from across the pond, the EL34?
"To me, the best characteristics of the EL34 are a nice tight crunch in the upper mids and a throaty growl in the midbass. These are essential for a great mid-70's Plexi sound. 6L6s have a big, warm, balanced clean tone and a creamier overdrive with thicker mids. In equivalent circuits, these tubes both have a softer attack and less punch than the big-bottle tubes, and both sound particularly great when cathode biased. Regardless, they have very distinct sonic characteristics.”
But Bartel notes that the demand for low-powered amplifiers over the past two decades has brought forth a challenge for designers: how to capture those timeless, cranked-up tones at volumes acceptable for bar gigs, home studios, and hobbyists looking to avoid a noise complaint from neighbors.
6V6 vs. EL84 Tubes
Enter the 6V6 and EL84. Made famous decades ago by the Fender Deluxe Reverb and Vox AC-30, respectively, the demand for low-powered, practical amplifiers opened up a world of creativity for designers such as Bartel.
"The 6V6 is one of my favorite tubes. In general, it has a balanced, open sound with soft compression and just the right amount of transparency in the top end. Its overdrive sound is thick and warm in the mids, and not too glassy on top. Although it's mainly associated with amps like the Deluxe Reverb, you can make a pretty good Plexi with 6V6s,” said Bartel, adding that he's used the tubes in some of his flagship designs, like the Imperial, Comet, and Meteor.
"EL84 tubes have more harmonic content in the upper midrange and can be magical in the right circuit. To me, their best characteristics are their midrange chime, shimmer and glassy top end. They can be a little lean in the bottom end, but this helps prevent ‘farting out’ when pushed hard into overdrive.” Bartel recently used a set of EL84s in his new design, the Royalist, to capture the tone and feel of the legendary Marshall JTM45. The JTM45 originally ran off of a pair of EL34 variants known as KT66 tubes.
"I put a lot of effort into the design of the output stage and power supply of that model to force a pair of EL84s to sound more like EL34s. In the end, I think you can still hear some of the EL84's chime and top-end transparency, along with some of the EL34’s growl and punch,” he said regarding the Royalist.
At the end of the day, some tubes are simply better for certain tones than others.
"The EL34 is the only tube that really nailed the vintage Plexi tone in the Royalist. Even considering all of the special effort that went into the circuit design, this tube choice is critical. It has a unique harmonic profile when driven into distortion that other tube types just can't match,” said Bartel.
"On the other hand, there are cases where 6L6s sound very similar in character to 6V6s. For example, the Sky King (6L6) and Imperial (6V6) are quite similar in their general tonal characteristics,” he noted.
Bartel also said that there can be significant differences between brands of the same tube type. Once players establish the type of tube they favor most, they can use their ears to hone in on the tone they’re looking for.
"The choice is purely a matter of personal preference. For Tone King amps, I choose the tubes from brands that I personally prefer, but I don't presume that they'll be the best choice for everyone. I like the TAD 6V6 in the Imperial amp because it sounds more like a good NOS 6V6 with a smoother overdrive and a softer feel. For folks desiring a more powerful sound, I suggest JJ 6V6s because of their tighter, more powerful attack with less compression.”