Before the microchip, before the printed circuit board and the field-effect transistor, we made sound with fire. Around the turn from the 19th to the 20th century many people were working on transconductance or the ability to amplify a weak signal into a powerful current. In essence they were taking Edison’s light bulb a step further and using it not to heat a filament to create photons, but instead to “create” a flow of electrons: electrical current.
A man named Lee de Forest won the usual patent lottery in 1908 – 1919 to be named the “father” of the vacuum tube. As was usually the case at the time there were numerous lawsuits and countersuits, and de Forest came-out on top but only after selling his rights to his invention to pay his legal bills. But what he invented (along with all the nameless others who were working in the same field) revolutionized almost every facet of daily life.
The first vacuum tubes were called diodes because they had two elements: the cathode is an emitter that “boils-off” electrons when heated by electric current. These negatively charged electrons are repelled by the negatively charged cathode, and jump across a tiny gap to the second element in the diode, the anode. The positively charged anode captures the loose electrons and passes them along as current. The neat trick is there is more current passing through the anode than was used to heat the cathode. This is due to inherent capacitance in the cathode emitter – it “holds-back” electrons as much as it can, building-up a charge that is then released across the tiny gap to the anode.
The upshot: you amplify a signal by running it through a diode – but not much. What Lee de Forest did was discover that if you add a third element that sits in-between the cathode and anode, and give it a negative charge, it will block electrons from flowing from the negative cathode to the positive anode. Increase the negative current up toward the positive range, and the electrons not only flow freely but much more of them flow more quickly. This third element was called a grid, and this new three-element tube was called the triode. The triode, along with its later siblings the tetrode and pentode, became the foundation of modern electronics in the first half of the 20th century.
The Guitar Amplifier’s Roots are in Radio
There are very few solid-state guitar amplifiers that are considered classics: the Roland JC120 comes to mind. But the JC120 is an example of a machine designed to do one thing and do it well: deliver clear, clean, undistorted signal at the speaker outputs. After that the only distortion you can hear is the inherent speaker distortion. There can be very little speaker distortion when a speaker is new, but it will increase with the speaker cone’s age. The JC120 worked well as an output amp for the Roland/BOSS line of digital amplifier modelers like the GT-8 because it adds so little of its own tone to the sound it’s kind of “clinical” sounding. Jazz players like it because it’s clean, it’s pretty loud if you want, and it doesn’t color the input signal much.
The reasons tubes have survived in audio applications are because they are inefficient, only loosely within spec, and they douse the signal passing through them in color. That “color” is a sum of distortion + capacitance + unpredictable oscillation + circuit noise. Just about all the things that make transistors a better choice over tubes are exactly the things that make tubes the best solution for amplifying electric guitars.
Of course the principal consumer market for tubes was radio. In radio, whether transmitting or receiving, there should be as little noise or distortion as possible. The ideal to be strived-for in just about all vacuum tube circuits was clarity and low noise. Expensive radio console sets had excellent amplification and sound quality. Cheap radios would distort when played loud, and had noticeable signal noise under the crackle of their poor reception. So when it came time for electrical engineers to design guitar amplifiers they took that mindset with them. The early history of the guitar amplifier is a constant striving for brighter and clearer tone. But at the same time the Great Depression was on and so a lot of early pickup/amplifier sets were cheaply made. The pickup was attached to the guitar – sometimes using bolts – and had a cable lead running to the amplifier. Some of these setups were hard-wired and you couldn’t detach the lead from the pickup or amplifier. But there was no real consumer market for these products so their production quantities were low compared to modern standards. There were probably more professional musicians in the 1930s than there are now. Without the opiate of television to incarcerate them in their easy-chairs, people actually attended events with live music quite often. But no one was getting rich making electric guitar amplifiers, not even Gibson or Gretsch.
The guitar wasn’t really a very popular instrument. If you wanted to be heard you went for something with natural amplification like a trumpet, trombone, saxophone, or even clarinet. There wasn’t enough energy available in using the hands to vibrate strings to push that sound any distance at a competitive amplitude: in other words guitars weren’t loud enough. They were a rhythm instrument used by solo singers, in trios, or buried in the rhythm section of a band.
It was after World War II that the guitar became a popular instrument used in the smaller bands of the era. It came forward from the rhythm section to the lead, and spread out from its country-western and blues roots into all pop music genres. And people in the music business got serious about amplified guitars because the general public was becoming an important customer. The old speaker-and-a-plug steel guitar amps were improved and given new features like tone controls and an on/off switch. New pickup designs became an integral part of acoustic guitars designed to be amplified. The guitars themselves began to change as they were adapted to being primarily electric instruments.
Tubes are Touchy-Feely
Very few people would dispute that Leo Fender is the key person in electric guitar amplifier development. He started making them in the mid-1940s for lap steel or “Hawaiian” guitars. If you look at his work over the years you see the modern form of the amplifier emerging in his designs until in the 1960s he perfected them, I think as far as most electric guitar players are concerned. The row of controls on the front-mounted “faceplate”; the addition of separate tone controls for bass and treble; dual channels, one as clean and noiseless as possible, the other with more bite, and often tremolo and spring reverb effects attached to the signal chain. Leo was an old radio man, so he built his amplifiers like his radios: as simply and most importantly as economically as possible.
When you turn on a big amp like a Fender Twin Reverb it takes perhaps 20 or 30 seconds for the tubes to warm. Compared to transistors tubes are gigantic and their reactions to voltage differences in the input signal are not instantaneous. It really depends on how much juice you are pushing through them. There is a point, usually somewhere between 3 and 7 on the volume knob of a Fender, where you will find a “sweet spot” where your particular amp is at it’s most responsive to dynamic changes in your playing. This is that sense of the guitar being alive and participating in the playing that most players live for. And it’s mainly about finding the right combination of volume and tone controls to make the tubes ramp-up amplitude when a string is struck, rather than immediately starting at the attack like solid-state circuits do. Tubes oscillate depending on the frequency being fed to them. These characteristics give the guitar a sort-of detached personality of its own, and your job is to adjust your playing to use this irregularity in response as a creative tool. Sometimes you feel as if you are just nudging the instrument in the direction you want it to go, and you use a light touch that lets the strings ring with sustain even after you change fingering for the next chord. And sometimes you’re bending and vibrato-ing your brains out because the feel is sharper and the strings need be hammered a bit to get the attack tightened-up. And you’re doing all this stuff at the same time because the sweet spot is so rich in harmonics and so responsive to your playing your playing is better.
For years I only played through transistor-based amps because you can disconnect the speakers without damaging the transformers and circuitry.* So I used a lot of Peaveys and simulators like the BOSS GT-8 and the Vox Valvetronix box. The first time I played a real tube amp I was hooked. The level of response to touch is so much greater, and more interesting in its sonic character, that transistors and microchips now seem limiting (although some of the new modeling amps like the Mustang V are pretty amazing simulations).
In the final paragraph (which is this one) it all comes down to what you like. Many players like the immediate and consistent frequency response of transistor amps. Even I will at times trade-away tube-heaven for a modeling amp because of convenience (the Red Twin weighs a ton!) and the need for sounds a clean-minded Fender can’t make (sometimes it takes a jangly Vox or a full-on distortion machine like a Peavey 5150, or a crunchinator like a Marshall. While the modeling amps and pedals sound different, they don’t sound like tubes. Or maybe I should say they don’t feel like tubes.
* Tube amps have to “see” an electrical load at the speaker end of the power section. This is why you must use an attenuator of some type if you want to use an amp like a Twin at a bearable practice or recording volume. Many of these boxes actually have a speaker coil inside them that lets the amp see the load it wants, but that makes no sound because there is no cone.