Beginner's Guide to Tube Equipment Upkeep
By Chris Loeffler |
(Note: Tube amplifiers contain potentially lethal voltages, and any internal work—such as voltage checks, soldering, and even internal cleaning—can pose safety concerns and should be done by a professional.)
Tube and analog audio devices defined the sound of electric instruments for more than a half a century, and has become so ingrained into the general concept of what an instrument sounds like that even in the year 2017, where all technology is heading digital, most players have stuck to tube amplifiers - or at least digital or solid-state audio processing that replicates the warmth and unique gain structure of tube-driven circuits. Unlike most modern consumer electronics, tube amps leverage antiquated technology whose “flaws” and technical limitations are actually considered a benefit. That said, like any device using physical components, tube devices require regular upkeep to maintain peak performance. Proper care is neither time consuming nor prohibitively expensive.
Regularly played tube amplifiers likely require changing at least the power tubes (and probably the preamp tubes as well) every couple of years or so. You’ll know it’s time to consider a re-tube when you experience inconsistent volume/gain levels between uses, increased hiss and white noise, ora general dulling of tone. Re-tubing most amps is something players can do with no experience or equipment, although there are fixed-bias amps that require rebiasing when output tubes are changed, meaning a multimeter or a professional is required.
On the average, output (power) tubes tend to benefit from replacement every couple of years, although how often they're used and how hard they're pushed impacts that estimate. Preamp tubes generally last longer, with the first preamp tube and phase inverter positions being the most likely areas to need attention if the amp begins sounding dull. There’s a long-standing rumor that handling tubes with bare hands leaves oil on the glass that can create hot-spots and result in early failure, but that’s not really accurate (although working on anything with clean hands is a good idea)! As always, be sure to follow your amp manufacturer’s owners manual’s instructions for tube replacement, and use higih-quality, properly tested tubes as your replacements.
Guitar amplifiers (especially combos) go through quite a bit of physical stress from transportation and even the physical vibration of the amplified noise passing through the speaker. To stay on top of this, physical maintenance to keep your amp firm and rattle free, like tightening speaker-mount nuts finger-tight should take place every three to six months. When tightening speaker mounts, the goal is to create a solid connection between the speaker and cabinet without getting so tight you’re bending the speaker basket or damaging the wooden baffle to which it’s mounted. Following this same approach, check the mounting screws or bolts holding your transformers to the chassis, the speaker baffle, the back panels on the cabinet, the handle, the feet, and even the chassis itself. Anything that is loose can (and will) rattle when you crank up that amp .
Electrolytic capacitors (filter caps) keep electric ripple and noise out of your amp’s power stage, and are likely the second-most short-lived components in your amp. Quality filter caps should last between 10 to 20 years before beginning to fail. Faulty filter capacitors result in noisier operation and a flabbier-sounding low end; at the point of near total failure, they can introduce dissonant harmonics that sound a little like a lower and out-of-tune tone. Due to the need to know basic soldering for extraction and their proximity to high-voltage circuitry within the amp, replacing filter caps is likely a job for the professional amp tech. To be clear, a dangerous charge can be lurking in your amp even when it's switched off and unplugged, and this charge can persist for a while. The parts themselves are not expensive, and a quality tech with a schematic of the amp for reference can likely replace them in 15-20 minutes.
While modern amplifiers tend to be built with more tightly spec’ed parts than their vintage brethren, resistors in amps old and new can drift in tolerance over time and sometimes fail entirely; this is another job for an experienced electrician. Crackling, hissing, and sizzling sounds, particularly during warm up, are all signs the carbon comp resisters in your preamp may be failing. Larger resistors in the power stage also occasionally fade due to the heat and high voltages they handle. These aren’t in the signal chain, but they’re worth having a tech test them if your amp is being serviced for anything else.
Does this basic maintenance sound like too much? It really isn’t. It’s a small price to pay to keep your tone a great as the day you bought the amp. If your guitar started sounding dull, you’d change the strings. If your intonation started drifting, you’d have it set up. The same should be true for your tube equipment; if you love the sound of your amp, make sure it keeps that sound over the years! -HC-
Things to Know
A vacuum tube, like a light bulb, operates by heating a metal filament (cathode) coated with electrons, which emits them to the plate and become a moving electric current.
If too many electrons heat the plate in the tube, it will eventually overheat and be destroyed. By applying a bias voltage to the grid, the number of electrons passing through the grid is reduced and can be managed for optimum performance.
- Tubes need to be biased correctly. If they are biased too hot, your tubes may be running beyond spec and die prematurely. Set too cold, your tubes may sound lifeless and sterile. As tubes are often run in pairs, biasing them equally (to the manufacturer’s recommended level) prevents one tube from working harder than the others.
- If your amp has a standby switch, let the amp warm up for 60 seconds on standby before turning it up to full power. If your amp doesn’t include a standby switch, avoid passing any signal through it for a similar period of time. Until the tubes have warmed up and are in optimal operating mode, processing an instrument's signal is overly taxing on them.
- Tubes turn white when they lose their vacuum, which is a good indicator that they need to be replaced. Another visual clue is purple glow focused around specific elements. This glow, which means there is leakage, can be confused with the combination of orange glow at the filament and the cloudy blue glow near the glass.
Chris Loeffler is a multi-instrumentalist and the Content Strategist of Harmony Central. In addition to his ten years experience as an online guitar merchandiser, marketing strategist, and community director he has worked as an international exporter, website consultant and brand manager. When he’s not working he can be found playing music, geeking out on guitar pedals and amps, and brewing tasty beer.