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Guitar amp tubes have become so common place for us, yet I’m often amazed by the many myths and misconceptions surrounding this relatively simple technology in terms of how to care for and extend the lifespan of these fragile components. With so much confusion and misunderstanding of the basics, you can end up with an amp that isn’t living up to its full potential. You can also spend a lot of time and money continuously replacing tubes, or worse—you can damage your gear. So, let’s address some of the fundamentals of tube and amp maintenance, which, if understood and applied correctly, can extend the longevity of your tubes and ultimately ensure the best possible sound out of your amp for years to come.
Basic Tube Architecture
Since most of the points I will make directly correlate to the technology itself, the following is quick synopsis of how a tube works (without getting too technical): A vacuum tube, which is somewhat like a light bulb, operates on the principle of thermionic emission. When voltage is applied, a metal filament coated with electrons, known as the cathode, is heated and emits some of those electrons. The electrons hit the plate and become a moving electric current in a wire. This current can do useful things, such as push a speaker cone to make sound.
The Importance of Tube Bias
As you can imagine, there are many electrons moving through the tube, hitting the plate and causing it to heat up. If there are enough electrons heating it up, it will turn red-hot, melt the tube’s glass and the tube will be destroyed. To prevent this from happening we apply a “bias” voltage to the grid, which functions like a sieve and reduces the number of electrons passing through the grid.
You can think of the bias voltage as window blinds; you can control how much light gets through by adjusting the blinds.
With the basics out of the way, let’s take a look at some tube tips:
1. Make sure your tubes are correctly biased. Setting the bias on your amp is analogous to setting the idle on your car. If it’s set too high, the car wants to run ahead, but if it’s too low then the car will choke when you apply the gas. In guitar terms, set the bias too high (or “hot”) and your tubes may run over their spec and die prematurely. Set the bias too low (or “cold”) and your tubes may sound cold and sterile. When working with pairs or multiples of tubes, you also want to make sure that they are equally biased to the same level (or to the manufacturer’s recommended optimum bias level) to prevent one tube from working harder than the others, thereby shortening its lifespan. (See figure below.)
2. Turn on the main power switch first and let the amp warm up for at least one minute before turning on the standby switch. This step alone can greatly increase the life of your tubes. Standby is a state of equilibrium for your amp. The speaker remains inactive, but preamp and power-amp tubes are given a warm-up before being subjected to heavy use.
3. Operate your amp at room temperature. This is a “common sense” tip, but make sure your amp tubes and components have fully adjusted to room temperature before turning the amp on.
4. Keep all liquids and beverages away from your amp—liquids and electricity don’t mix. Accidental spills can not only ruin your gear but can also cause fatal injuries!
5. Replace your tubes when needed. Tubes turn white when they loose their vacuum, which is a good indicator that they need to be replaced. Another is when your tube amp starts sounding loose and weak. Although these are subjective terms, when you’ve grown accustomed to your amp’s tone, you’ll notice when this happens.
A good tube amp is designed to last for years, and if you properly follow some of these basic principles for maintaining your amp’s tubes, you’ll keep your tone and peace of mind intact.
Yuval Fuchs has been an audio engineer and guitar player for 26 years. He is currently a Senior Sales Engineer at Sweetwater Sound, and spends his free time testing new pro audio gear and tinkering with guitar parts. He can be reached at firstname.lastname@example.org.