Until the transistor came along, electronic amplification was produced by vacuum tubes.
These tubes were in TV sets, radios, hi-fi sysytems, and guitar amplifiers, and were also vital components of military applications like radar. In almost all these devices tubes have been replaced by solid state technology – that is, semiconductors – except in some guitar amplifiers. And that’s because to a lot of guitarists, there’s no replacement for the sound produced by tubes.
A tube is just a vacuum-sealed glass bottle with an electrode that emits electrons when heated (cathode) and an electrode that attracts electrons (anode). It also contains a grid, which modulates the flow of electrons, and a filament, or heater.
Dave Hunter tells us that when a guitarist plucks a string on his guitar, the pickup sends a small voltage to the input of his amplifier, where it’s passed along to the grid of the first preamp tube. The grid creates an increase in voltage by causing electrons to “boil off” the cathode, making the sound bigger. This bigger signal is passed along to the output tube, which makes it even bigger. This is then carried to the speaker via the output transformer.
Some listeners can’t really tell the difference between a solid state amp – or transistor amp – and a tube amp. But for many guitarists, tube amps are the only way to do it. Danny says that a solid state amp produces a clean, crisp, accurate sound and that it’s quick and responsive to your playing. It requires less maintenance and can emulate many different amplifiers at the push of a button.
The downside of a solid state amp is that the sound lacks “warmth” – it’s usually cold and sterile. Distortion is too sharp sounding. There’s no individuality to the tone and all amps will sound the same with almost any player.
Tube amps, on the other hand, are best known for their warmth, he says. They are pleasing to the ear. Scientists can’t measure the warmth, which is probably why they haven’t been able to duplicate it in a solid state amp.
Also, each tube amp sounds different, with its unique tone. No two guitarists will sound the same through the same tube amp, as the amp will respond to each individual’s playing technique in a different way. Tube amps sound fat and thick, and will sound even fatter as the volume is turned up, creating that famous wall of sound.
Tubes distort sound, compressing the sound in a most pleasing way. The transformer can’t handle the signal peaks and softly rounds them off, causing even more distortion (a good thing, he insists).
There are disadvantages to having a tube amp, though. Danny says that it doesn’t sound good at low volumes; it’s best to play it loud. Tube amps also cost more than solid state amps. And you need a guitar pedal to create different sounds. They’re also very heavy.
Some features of tube sound can be produced in a digital filter. Engineers have developed transistor amps that emulate the sound of a tube amp. Tom Scholz, rock musician and mechanical engineer, introduced the Rockman, which used bipolar transistors but created a distorted sound that some musicians like. Rockman technology was used exclusively for Def Leppard’s album Hysteria. You can also hear it on Eliminator by ZZ Top.
And yet for many guitarists, nothing sounds like tube amps. Many of these purists are great fans of Roger Modjeski, who’s been designing tube amplifiers for almost his entire life. He says that his design career began at 11, but he gained his first knowledge of tube amps at the age of 5, watching his father build a Heathkit Mono hi-fi system. Modjeski himself built a dozen hi-fi sets from Heath kits while growing up. And then:
Around 1964, my interest and the industry’s turned to the new “miracle” transistors. I, in my basement shop, and the giants of the industry all did our best to design good-sounding amplifiers with these new devices, and we all failed.
But Modjeski continued experimenting with transistor circuits and invented a few of his own. In 1969 he went to the University of Virginia to get his degree in electrical engineering, learning that he was the only one in his program who had built his own amplifiers. After graduating he got a job at IBM but he saw it as a dead end. He opened an audio repair shop in his hometown of Richmond, Virginia.
In 1975 he went to Stanford to get a Master’s degree, but after a year he gave up on it and returned to Virginia. He got to know Harold Beveridge mainly by being his dealer in Virginia, even though he had met Beveridge at Stanford. Harold Beveridge was an electrical engineer who had attended McGill University and then worked for Raytheon before designing amplifiers.
In 1978 Modjeski went to work for Beveridge as a consultant and later as Chief Engineer. He designed tube amps there but left after 3 years, and by 1981 he decided to start his own company, Music Reference. On his website you’ll read that MR products are known for their ease of use, reliability, and longevity. His company Ram Tube Works was established in 1982 and was the first company to offer premium tubes tested by computer. You’ll learn that several other companies have tried to take their market and failed.
Roger Modjeski has a separate concern, however. He is asking, “Where is the next generation of audio engineers?”
He says that for 20 years he has put out the call for young people to come and work for him. A few have come, he says, but as the years go by, they are fewer and fewer. He has run ads in Stereophile to get the attention of young people interested in science and inventing, and done the same in his comments and on his website. He’s gotten little reply, he says.
He was an apprentice under Harold Beveridge and he has served as a mentor himself. But not enough people are showing interest in the field. “If you truly love audio, what else are you doing that is so much more important?” he wonders.
The industry needs new talent.