Some guitarists religiously replace the tubes in their amps every two years; others never do so, or not until the amp takes a vow of silence. The two camps don’t exactly see eye to eye, and their preconceptions and differences of opinion are fuel to the flames of debate raging in many forums. We’d like to shed a little light on the topic to banish the darkness from the great tube-swap controversy.
So does it pay to regularly swap tubes?
Playing guitar at home has never been as convenient, rewarding and motivating as it is today. It’s always been a treat to revel in the sonic glory of bona fide tube-flavored tone. Now, though, thanks to innovative technology we can do this even at low volumes in the comfort of our cribs. Some modern-day tube amps deliver stunning sound at low wattages. And if they’re equipped with a power soak, a circuit like the TSC to protect tubes, and a DI out such as the Red Box, they offer reliability, utility and outright convenience few would have thought possible just a few years ago. This all adds up to countless hours of bliss for guitarists. But the clock is ticking, and sooner or later some will begin to ponder how much life is left in those tubes. So let’s talk about how many operating hours of rocking good fun you can expect to enjoy and when it’s high time to retire your old tubes.
Many tube amp owners, unaware of the facts, are overly cautious, guarding the heart of the amp – the power tubes – like a mother hawk watching over her eggs. Tubes are not as fragile as eggs, but like hatchlings, they do need some tender loving care. A little healthy curiosity goes a long way: It behooves guitarists to learn more about tubes so they can do a better job of looking after them. As discussed in the VTI blog post, tubes – and those big power tubes especially – are exposed to heavy electrical, mechanical and thermal loads. If you’ve ever touched a working tube with your bare hands, you’ve felt the truth in that. Any component that takes that kind of battering is not going to last forever. It will have to be replaced eventually. The consensus among connoisseurs of tone is that a creeping deterioration of the amp’s sound sets in as soon as tubes are past their prime.
When is eventually?
First let’s debunk some of the myths. There’s no voodoo at work here. Good tubes may get your mojo working, but swapping them when they’re on the brink of zombification – the lights are on, but nobody’s home – won’t mess with your juju. The facts aren’t easy for some of us to face, but in the sober light of day our beloved tubes are just wearing parts like the brake pads of a car. Most of us don’t cling to those for sentimental reasons; we change them when the sparks start flying. On the other hand, aging tubes are not the tone-sucking demons that some people in many forums make them out to be.
The tubes in an amp live shorter lives than semiconductors. That explains all those sockets in the chassis. Guys and gals who earn their living with a soldering iron will tell you that hardwiring tubes into the circuit would be a much better option if technical concerns alone mattered. Better, yes; feasible, no. Swapping tubes with a hot soldering iron is not the sort of pastime most of us envision for ourselves. But I digress. You may find it reassuring to learn that there are tubes that do their job without complaint for decades, so most concerns are unfounded. And with a little background information, you’ll know all about the few truly important criteria that prompt a tube change.
The first criterion is a tube’s maximum life expectancy. Even the most mathematically challenged player should be able guesstimate how much of that life has been expended. We’re not talking about the shelf life of a perishable item here. The only thing that matters is how many operating hours it has put in, and not how many years have passed since it what was made. You can expect a conventional amplifier tube to have a service life ranging up to 10,000 hours. Tubes with military specifications are built to last up to 100,000 hours. How do you know if you’re looking at a military-grade tube? You could say that the type designation made a military maneuver and shifted to the right flank: ECC83 is the designation for the regular civilian tube; E83CC denotes the military version.
On the left is an ECC83 tube, on the right an E83CC, a military version that is made to tighter tolerances and lasts longer
Here’s a little arithmetic for the worst-case scenario, or as we musicians call it, gigging life:
Two rehearsals a week lasting two hours each + two gigs a month lasting three hours each = 22 hours of operation a month. Let’s round up to 25 hours a month just because we like to play. 12 x 25 = 300. Now we have a rough idea of how many hours a year those tubes get toasty.
The 10,000 hours of expected tube life is of course an estimate, but not an unrealistic prospect. If we divide this life expectancy by 300 hours of service a year, we get a useful life of 33 1/3 years. Now that has to come as a big surprise. And what’s even a bigger surprise is that some tubes whose life isn’t cut off prematurely by some unexpected mishap or malady actually gets the job for that length of time. Even if we take the pessimistic view and say our tubes are only going to hold up for half that time, we’re still talking about fifteen years. Yes, some tubes fail much earlier than that, but many indeed last that long. That’s a number most of us should be able to live with. The bottom line is that tubes are far more reliable and faithful companions than their reputation would lead us to believe. So while some may practice premature tube replacement as a precautionary measure or to tweak their tone, it’s only a technical necessity when the tube is ailing or failing. This is why it’s not unusual to come across fellow travelers on the road toting amp heads with their original ‘60s and ‘70s tube complement intact and still sounding sweet. What’s more, we’re talking about power tubes here. Preamp tubes are more compact and don’t have to work as hard, so they tend to last even longer, or seemingly forever if you’ve been waiting for them to go bad so you don’t need any excuses to try a new set. So when does a tube swap become a necessity?
The most compelling and immediate criterion for tube replacement is any corruption of the tube’s vacuum simply because the consequences can be dire. This corruption can be slow and insidious as is the case with thermally induced hairline cracks or as abrupt as a burst or broken glass envelope. Both cases are extremely rare and usually occur in tubes that have some previous damage or are subjected to extreme mechanical duress, for example, when your well-meaning buddy drops your amp. You can determine if the vacuum is intact by examining the getter – that’s the metallic-, chrome- or silver-colored layer at the top of the tube – to check if it’s milky or discolored. If you spot discolorations or see that the entire top of the tube is stained with a milky coating, than air has entered the tube. It is defective and must be replaced.
This EL34 tube sucked some air. The vacuum is history; the getter is white and milky, a sure sign that the tube has come to a sad end. This doesn’t mean it gets buried in the bin with the potato peelings. Defective tubes should be disposed of properly like all other electrical components
The second case that would make a tube swap at least worth considering has to do with dirt and residue sealed inside the tube when it was made. They can be time bombs that upend gigs with their nasty surprises. If you’re lucky, these particles will at some point be burned in place. On a not entirely unrelated note, the VTI system does this automatically while tapping the tube, which is why Hughes & Kettner tubes are safe in this regard. If foreign matter is burned in, the tube will be reliable and you will on the safe side. If not, the worst case is that it will short-circuit and silence the amp. Incidentally, this explains the oddity of all-tube amps failing either very early or not at all. Loose particles in a tube can be a problem for a new amp, but they’re usually burned in place during the first hours of operation. They will no longer be an impairment once they’re fixed in place and the life of the tube will vary only slightly from that of a pristine tube.
Wear, oxidation inside and aging are the logical consequences of operation. They can be detected, but their effects are not nearly as audible as is commonly believed. The degradation is gradual and very slow, so the sonic consequences are going to be difficult if not impossible to discern, at least in the early stages.
So if concerns about the life of a tube have been keeping you awake at night you can rest easy now. They do tend to last longer and operate more reliably than some would have us believe. Defects occur either very early if any residue inside is not burned in, or when they can be expected to occur because the tube is approaching the end of its service life. Problems with the vacuum inside the tube are extremely rare. Swapping tubes before their time is a fruitless exercise unless it’s done to change the amp’s voice. And if your amplifier is equipped with device like the TSC module found in Hughes & Kettner amps, then it won’t even need biasing after new power tubes have been installed. If it lacks such a device, you should leave the task of swapping power tubes to professionals who can also match them and bias the amp properly. We hope this news dispels all the concerns about tube’s reliability and any maintenance related anxieties. All-tube tone is not some luxury for a select few to enjoy. It’s there for everyone, even technophobes, to take pleasure in.
Hebra Definition 
