Tube Reliability & Warranty

Most mechanical issues in new electron tubes appear within the first few hundred hours of use. For example, tiny glass microcracks may stay stable for years but can cause vacuum leaks after around 500 hours. If a tube performs well beyond that, it’s unlikely to fail later.

Many vendors offer only a 3-month warranty — often too short to cover 500 hours of use. At EML, we provide a 12-month (or 2,000-hour) standard warranty, extendable to 5 years through online registration.

Our extended warranty also covers vacuum defects, ensuring lasting reliability.
After registration, you’ll receive a personalized confirmation with your tube’s serial numbers and warranty details. Your email is used only for this purpose and deleted once it’s no longer needed.

Safe Operation

Like all electron tubes, higher anode dissipation or current means shorter lifetime. For the best balance between performance and durability however, it’s good to stay below 75–80% of the maximum anode dissipation, and for longest life, aim for around 60%.

Some tubes are designed to run safely at full power without reducing lifespan — you can spot these when the datasheet lists the same value for typical and maximum dissipation. For example, the RCA 2A3 (and EML versions) can be used at full rating with no impact on life. Others, like the Western Electric 300B (and EML 300B), will last longer when operated a bit below their maximum rating.

Lifetime

The best lifetime will occur at the specified heater voltage, a safe electrical circuit, no crude start up, and no oversized capacitors for rectifier tubes. Also coupling capacitors can shorten lifetime if dimensioned for a few Hz only, which can create positive grid current during start up.

The Anode current is factory tested after initial burn-in. This level is called 100% when the tube is new. This is an individual value for each tube, and the required Control Grid Voltage for this is written on the tube box. If you wan to judge the condition of an older tube, you should test it at just that same Control Grid Voltage, as we measured when the tube was new. It will stay at or close to that level during customer burn in. In the beginning the Anode current can change (up or down) very slowly, or stabilize for most of the time. After it stabilizes, the customer burn in is finished, and normal wear out will start to begin. You will observe the Anode current going down very slow, each few hundred hours. So if the Anode current (referring to the original test value) has decreased, this is a normal sign of use, and no defect. This will continue during the entire lifetime. Amplifiers with Auto bias, will hold the Anode current fairly good. Amplifiers with adjustable bias, will need regularly adjustment. That's what the adjustment is for, because these have no Auto bias. When the end of lifetime is getting nearer, the Anode current will start to go down quicker than before. Generally, you can say when the tubes sound good, that's what they are. Only you can not judge the remaining lifetime in the tube by that. On a test bench, the measured values of fairly used tubes can be at 70% Anode current. There is a general conception that such tubes have still enough lifetime left in, to make a well designed amplifier function normally. This value of 70% is found on most tube testers as the level where the 'good' reading begins.

For the best tube life, use the specified heater voltage, a safe circuit, gentle startup, and correctly sized components. DC coupling, oversized rectifier capacitors or low-frequency coupling caps can stress the tube and shorten its life.

Each tube’s anode current is factory-tested after burn-in and marked on the box. To test an older tube, measure it at the same control grid voltage used at the factory. During customer use, the anode current may shift slowly at first, then stabilize. A gradual decrease over hundreds of hours is normal, showing typical wear — not a defect.

Amplifiers with auto-bias maintain stable anode current, while manual-bias amps require periodic adjustment. Toward the end of a tube’s life, the anode current will drop faster. Tubes may still sound excellent even with reduced current. On many tube testers, 70% of the original anode current is considered “good,” meaning the tube can still perform well in a properly designed amplifier.

End of Lifetime

This becomes audible, when the tube starts to distort at loud music, and was not doing so before. When you can measure the Anode current, the area for a 'good' tube is above 70%. Below this is not always the end of lifetime, or a bad tube. Tubes with values of 40% have been reported to work normal, depending on the amplifier. Below 40% problems will probably occur. So you can feel safe when buying used tubes at or above 70%. Not below that.

What causes long tube life?

Provided, the manufacturer supplied a first class product, the user can contribute by respecting the condition of the cathodes (the heaters).

During normal use, the cathode must be so hot that electron emission takes place at a high level. Unfortunately this temperature is so high, that a small fraction of the Barium layer will evaporate by this. This gives small openings in the layer, and at these openings, the Barium Oxide layer underneath gets exposed to electrolysis. The result of the electrolysis is Barium Oxide (white powder) gets reduced to metallic Barium, and Oxygen gas. The Oxygen finds it's way to the getters, and the Metallic Barium closes the hole. This process is like a self repair. However after some time , the Barium Oxide layer gets depleted.

A carefull balance must be found.

So the cathode must be hot enough to give the emission, and also more heat gives more regeneration (calles electrolysis before). However the heat will also cause evaporation. So one way or another, wear out is unavoidable. So the regeneration must be as little as necesairy, but as high as needed.

Once this process is understood, it is clear we want two things, which seem to exclude f each other:

Keep Barium evaporation at a minimum level. (Reduce heat).
Create a self-repair process. (Increase heat).

In other words, over heating may seem to work nice initially but it will wear out the tube much faster. Under heating will greatly reduce wear out, but there is not enough regeneration. It comes down to using the correct heater voltage with as little tolerance as pissioble.

Any questions, like what heater voltage tolerance is allowed, we answer always like this: Zero tolerance is the best!

Over heating will must faster evaporate the Barium metal. Furthermore, over heating will speed up the migration of Barium from within the cathode. So from electrical testing, it seems as if over heating doesn't matter much. The tube seems to take it, and tests normally good afterwards. Yet this impairs lifetime very much. Overheating will empty now the Barium depot very fast, and when it is used up, migration will stop, the Barium layer will evaporate finally, and this time without repair. The tube life is over suddenly and unexpected.

Under heating. If the cathode is not warm enough, like when heating a 5V tube with 4.5V only, this is very good to reduce the Barium evaporation, and initially it seems like a good idea, since the tube works still normally, even below 4.5V. So users do not understand why exactly 5.0V is important. However the balance is disturbed, the migration in Barium to the surface is now a LOT lower. After weeks of use, the Barium layer gets too thin, and holes begin to appear. Now, soon emission will go down, the tube will sound distorted, and test 'defective' on a tube tester. If corrected timely, this damage will repair by normal use, at exactly the right heater voltage again. However if the loss of emission was only corrected by adjusting the bias, this will cathode damage becomes too large, and the tube damages permanently.

Balance. This the key and the secret of long tube life. So use just the right heater voltage, do not overheat or under heat the cathode. Do not overheat the anode, as this will effectively overheat the cathode as well by back radiation to the cathode. Do no draw excessive current peaks from rectifier diodes by using too large capacitors. Do not overdrive Push Pull amplifiers just for 'fun' to hear what this sounds like. All of these things will blow holes in the Barium layer, which need continuous repair. This uses up the depot faster.

Warm up. Make sure you have no circuits that draw peak current from the tube while the heater is not fully warm.

Very infamous for this are rectifier circuits with oversized capacitors. At warm up, the capacitors are initially empty. The rectifier must supply a high initial current to those capacitors, while at that same moment, the rectifier itself is not fully warm yet. This short moment (of overload) represents a wear out, same as a normal listening session. This is why is can not be repeated often enough, not to exceed the maximum capacitor value. This value is a safe limit, but anything above likely will shorten the rectifier lifetime.