Hello Troubadourians! At the end of the June column I wrote; “Tube amps can do this disappearing act, too. One minute you’re digging that fat tone you’ve spent years cultivating and the next minute you’d swear that someone has reached over and randomly turned the knobs on your amp. But that is a discussion for another time.” Well that time is now. For guitars, there are essentially two types of amplifiers: tube amps and non-tube amps. Yes, there are hybrid and digital amps in the non-tube category but that subject can get complicated and we’ll address non-tube amps in subsequent columns. I’ve found out from your feedback on previous columns that I can’t assume all of you understand every term I use, so I’ll start by defining what a tube is.
Wikipedia defines a tube as: “… a vacuum tube… is a device controlling electric current through a vacuum in a sealed, usually glass, container.”
Tubes have been around since the 19th century and were used in radios as early as 1906, but they gained popularity for guitar amplifiers in the 1940s. From the tweed-covered Fender amps in the ’50s, blackface Fender and “Plexi” Marshall amps in the ’60s, through the high-gain, multi-channel amps from Mesa/Boogie and others in the ’70s and ’80s guitarists have used tube amps to define good tone for a very long time. But tubes aren’t forever items. Tubes are like strings in that they are essentially consumable items. While their lifespan is considerably longer than strings, they do wear out and the useful lives of power tubes are especially limited. And, like strings, tubes can behave differently in different environments and under different conditions. Heat is essential for tubes to function and is also their nemesis.
Again from Wikipedia: “When hot, the filament releases electrons into the vacuum, a process called thermionic emission. A second electrode, the anode or plate, will attract those electrons if it’s at a more positive voltage. The result is a net flow of electrons from the filament to plate.’
As we play, the tubes will change their behavior depending on the how hard they are required to work from our playing, from external heating or limited airflow, or from exposure to direct sun in outdoor gigs to changes in the line voltage caused by voltage surges or sags. When playing in clubs, refrigerators, lights, and air conditioners can cause fluxuations in the line voltage. Outdoor gigs where the stage power comes from a generator can likewise wreak havoc with the voltage supply. These changes in the line voltage can – and often does – affect the function and tone of our tube amps. Usually, the first thing we’ll usually notice is a drop in volume followed by changes in the tonality. High frequencies are usually attenuated the most, effectively turning what once was rich tone into mud. As we soon find out, there isn’t a lot we can do about this phenomenon. Usually we’ll turn around and begin turning the knobs on our amps in the attempt to counteract the volume drop or tone change, but those sometimes frantic adjustments have little effect. Then, if or when the voltage recovers, we’ve fiddled with the controls enough that we’re suddenly too loud and our tone is too bright. Sometimes we chase this problem during the entire gig. (Line voltage fluxuations can be problematic for all electronic sound equipment.) So what can we do about this? The best thing we can do is to invest in a quality line regulator. Furman, Monster, and others make some excellent units.
I also need to address a subject near and dear to every guitarist; “My amp doesn’t sound good until I turn it up.” An excuse for playing loud or the actual truth? Actually, it’s some of both. As I’ve explained, tubes require three basic things to operate: voltage, current, and heat. Too much or too little of any of these three things and a tube will not operate at optimum performance. The volume and tone controls directly influence the internal voltage and current levels that the amplifier requires. The heat component can’t be controlled by the player directly. However, making sure that your amp has adequate space and ventilation for airflow to reach the tubes and doing what you can to keep them out of direct sunlight can help manage the heat. When we adjust the control knobs of our amps, we directly control the voltage and current that flows through the amplifier circuitry. The volume controls in particular have a huge influence on the voltage levels at work inside the amp. It is a proven fact that analog electronic devices work most efficiently in the center of their voltage range. For example, if an analog electronic device has an operational range of 0 to +10 volts, the device will operate most efficiently at around +5 volts. The upper and lower 20% of that operational range are significantly less efficient than the middle 60% of the operational range. In more familiar terms, that translates into having the effect of your amplifier sounding its best roughly between 3 and 7 on the volume control knob. Below that level, the tubes will not be operating optimally and above that level they usually don’t deliver much more amplification (volume), they just get hotter. Since power tubes operate at much higher internal voltages than preamp tubes, this effect is much more pronounced in the power section. This means that you need to operate the power section at a higher level that the preamp section to achieve similar efficiency – and therefore the best tone, the “sweet spot” – in both sections of the amp. The net result is that a higher powered amp, 50 watts for instance, will be much louder in the sweet spot than a 20 watt amp.
So, is it better to have a lower powered amp than a higher powered amp? No, not really. You need to have an amp that can operate in the sweet spot at a volume level that is appropriate for the venue. A good rule-of-thumb is that big venues and outdoor gigs require a more powerful amp than a small club. In the studio, an amp of 5 watts or less can sound bigger than a huge concert stack. Some of the most awesome guitar tones ever recorded were produced on tiny, low powered amps. Yes, your tube amp does need to be turned up to sound good but if you’re too loud, you just might be using too much amp.
Need to know? Just ask… Charlie (email@example.com)