Article by Andy Johnson -- Jun. 25th, 2020
For today’s discussion, we’re going to talk about a couple of variants of the 6L6 vacuum tube: the short-bottle 6L6 and the tall-bottle 6L6. What are they? What are their tonal characteristics? Why pick one over another? What are each of their unique advantages? We get asked these questions a lot, so we figured why not go ahead and lay it all out there?
A Little History...
Let's step back in time, to around 1935, when the first incarnation of the 6L6 came alive; it was then called the “Harries Valve.” This tube evolved gradually from an efficient tetrode (4 parts), into a beam pentode (5 parts) by the addition of an extra grid called the “suppressor.” This particular design was also marketed in Europe as a “Kinkless Tetrode,” as Phillips owned pentode-type tube patents in Europe at the time. This Kinkless Tetrode design was licensed to RCA, who hit the ground running with the design and, almost overnight, had implemented it into everything from radios, public address amplifiers, and communication equipment. The first version actually utilized a metal envelope, unlike the glass envelope we associate the 6L6 tubes with today. These original metal-envelope 6L6’s were good for around 19w, whereas the later 6L6GC (the most popular 6L6 design) were good for a staggering 30w.
The popularity of this tube, of course, pushed the evolution of the 6L6 to have more ruggedness, clarity, and fairly rapid power dissipation. This gave rise to not just a couple of 6L6 variants, but quite a few: 6L6, 6L6G, 6L6GC, 6L6WGC, 6L6WXT, 6L6WGB, 6L6CHP, and many others (not including it’s similar brethren, the 5881 and the not-so-distant KT66).
This brings us to the “Black plate” design 6L6’s. Implemented herein was a special “carbonized” coating coupled with the thick glass envelope that RCA had used to keep the plates in the tube cooler, extending the life of the tube. This blackened material did not really play into the overall tone of the tube, just it’s efficiency; however, I’ve had many long discussions with many techs disputing this point.
Now that we have a little history, we’re ready to discuss the 2 tubes in question: the 6L6GC (which are of the “tall-bottle” variant of the 6L6 introduced by GE as the GE6L6GC) and the 6L6WGC RCA/ Phillips “short-bottle” variant.
When comparing these tubes, the differences to most musicians' ears are subtle, but one can definitely tell there is something different between the two. Keep in mind, when it comes to comparing these two heavyweights of the tube guitar amp world, there is no such thing as “better,” just different.
The 6L6GC tall-bottle, throughout time, have been better-suited for classic rock and high headroom applications. These would typically be found in a Mesa, Soldano, Peavey, or even the occasional early Marshall. Characteristically, they are punchy and tight with lots of defined low end and later breakup than it’s shorter counterpart. We see these tubes flourish in finger-style fast-passage players as well as lap steel and some harmonica players. They compose themselves with slightly more crunch at higher volume levels, and are great to use with bass amps as well. They are currently in production as the TAD 6L6GC-STR “Blackplate,” JJ 6L6GC, Electro Harmonix 6L6EH and many others. With its rugged design it’s not uncommon to get two-thousand hours out of these tubes with only slight plate variation.
The short bottle “clear top” variant was used in many Fender tube amps like the Super and Twin Reverb, Tweed Bassman, Bandmaster, Pro, Super, 5E8-A Low Power Twin, etc. It gets the “clear top” name from having the “getter” structure on the side of the tube as opposed to the top, which makes these tubes instantly recognizable. They have a great musical property throughout the EQ spectrum. Easily pushed, these tubes overdrive with less effort than the tall-bottle, and have a tendency to be slightly smoother and slightly more compressed than their taller brethren. Additionally, these tubes don’t focus the tone to emphasize any part of the EQ spectrum. They are very well-rounded tubes with a very robust design. Again, it’s not uncommon to get up to two-thousand hours of use out of this tube. Unlike the taller 6L6’s, these had cooling vents cut into the plate structure as well as extended (wider) plate “wings” that acted as heat sinks for greater efficiency and prolonged tube life. This was one of Aspen Pittman’s favorites and he brought it back into circulation with his “clear-top” 6L6GE. If you happen to look at this tube, you will notice that the “getters” are on the side of the tube as opposed to the top and, like the taller GE versions, it has a taller glass envelope, but does have the inner-workings of the shorter WGC version. These are currently in production with the most popular being TAD 6L6WGC-STR “Blackplates,” and TungSol 6L6GC-STR.
Hopefully today's read has given you some insight as to how these different tubes operate, the differences in their construction, and what they can offer tonally. Each tube is, obviously, very well-designed and widely-used in the tube amplifier world. Thanks for tuning in, and we'll see you next time!