Photo by Andy Ellis.
Look at the back of any all-tube amp, and you’ll see warmly glowing glass bottles in a variety of shapes and sizes. Power tubes (aka output tubes) are typically the biggest ones of the bunch, and they provide the last stage of amplification for the guitar signal before it’s delivered to the speakers. The “power tube” name is a bit deceptive, however, because these big bottles don’t just power your speakers—they actually play a significant role in shaping your amp’s sound and responsiveness.
Regardless of its manufacturer, each power-tube type—EL34, EL84, 6L6, 6V6, 5881, etc.—has a basic sonic personality. Getting to know those tonal characteristics can be a huge help, whether you’re trying to track down a new amp with specific sonic traits, or just wondering whether you can change the sound and feel of an amp you own by using different power tubes (see the Swapper’s Delight sidebar).
To represent the signature sounds of the most popular tubes, I’ve relied on classic rock examples from the 1950s, ’60s, and ’70s. I don’t mean to suggest that tube amps are only good for playing classic rock. But during that era, there was a greater separation between American and British sounds. Also, players used few, if any, effects in those days, so you can often hear the sound of a guitar plugged directly into an amp, providing clear examples of the core sounds associated with each tube type.
Be sure to check out the power-tube comparison video we also created so you can hear the differences between each tube type.
Warning:All tube amplifiers contain lethal voltages. The most dangerous voltages are stored in electrolytic capacitors, even after the amp has been unplugged from the wall. Before you touch anything inside the amp chassis, it’s imperative that these capacitors are discharged. If you are unsure of this procedure, consult your local amp tech.