Tube Basics and Frequently Asked Questions
I have a brand new tube that's noisy. When I put my old tubes back they worked fine. This tube is defective.
Okay... I know this one's not really a "question" but we get it so often that it needs to be addressed anyway. Many times when a piece of tubed equipment is noisy, the cause is a bad connection between a tube and the socket, not a noisy tube. In fact, the majority of tubes we have returned to us for warranty replacement, are not noisy at all!
Remember: Tube sockets are not highly reliable connectors! If the sockets are dirty or not tight enough, or if the pins are slightly "thinner" than your original tubes, or have a little grime on them, it can cause one or more pins be unable to make solid contact. This can result in noise.
So... make sure your tube pins are clean before plugging them in. Also, make sure your sockets are clean and tight. Many times, just the act of removing a tube and re-seating it, either in another position or back into its original spot, can alleviate the problem. You might also try gently twisting the tube in its socket, to make sure it's getting a solid connection on all the pins.
How do I know when my tubes need replacing?
Power tubes like EL34's and KT88's are good for about 2500 hours or more. But may go longer in an amplifier with a conservative design. Small signal tubes with numbers like 12AX7, 12AU7, and 6922, and rectifier tubes like 5AR4 may go 10,000 hours. So you get years and years of enjoyment. Using a tube tester may or may not tell you if you need a replacement. The best approach is to buy a new set of tubes, and install them. If they don't sound a lot better, put in the old ones and suck every bit of life out of them.
What is the proper method for handling vintage tubes?
Many vintage tubes were labeled with ink designed to fall off easily. So do not touch it! If you get it wet at all, it may go away right in front of your eyes, and just shipping and pulling it in/out of the box can damage the logo. If the box is an original vintage box, open it carefully using a butter knife under the flap. The ends can tear right off easier than you would believe and some people prize the boxes.
As for the glass itself, despite what some people might tell you, the oil on your fingers will NOT damage the glass or leech through it. Tubes are not halogen bulbs. Tubes may get hot to the touch, but your finger oil will not cause the tube to break when heated up, nor will it affect tube life or sonics. It will not go through the glass.
What is the best way to compare my tubes?
We recommend not pulling tubes in and out a bunch of times to compare tubes. The best way to do this, if you really have to, is spend a day with one tube and another day with the next tube. We know it is tempting to pull them in and out a lot 'cause it's fun, but when you do, you may loosen the tube socket if you go in and out a few hundred times. Tubes, sockets, and tube gear are very durable. But use common sense. In addition, tubes need to be left undisturbed to sound their best.
My tubes flash at start-up. Is that normal?
Many European tubes in the 12AU7, 12AT7, and 12AX7 families may flash brightly when you first power up your gear. This flash is normal. It is also normal for the intensity of the flash to vary from tube to tube, and the flash intensity may also vary or even go away as the tubes age.
What is NOT normal is a flash from power tubes. If this happens at any time, turn off your amp immediately!
What's the best way to bias new power tubes in my amp?
If you are new to biasing… carefully read and follow the manufacturers instructions. Pay attention and make sure you are not in a hurry, stoned, or distracted. Even the most seasoned tube-head will tell you mistakes do happen. Remember, the voltages involved here are lethal.
When we match tubes, we are most interested in how the tube "idles" or draws current. Think of a power amp with four tubes as a car engine with four carburetors. If there is an idle adjustment for each "carb" that would be the same as an individual bias adjustment screw for each tube. If there is only one bias screw for each two tubes, you need a matched pair of tubes. One bias screw for each four tubes, you need the tubes in matched quads. If each tube has it's own bias screw, or if you have a PrimaLuna or Mystere amplifier with Adaptive Autobias, there is no need for matched tubes, though it certainly doesn't hurt.
Bias voltage is actually negative voltage applied to the grid to bring the tube to the idle point desired. That idle point is the one we read on a meter. Some manufacturers give you a specific point like 50 millivolts, or 50 milliamps. Make sure you use the right reading! Some may give you a range of say 40 to 50 or 55 to 65. The higher the number the tube is idling at, the hotter the tube is running. Running tubes with a hotter idle does NOT guarantee the best results. We always recommend biasing your amp to the setting specified in your amp's manual or maybe a little lower, but never higher. The engineers who designed your amp chose that setting for a reason.
This next section is extremely important! Danger Will Robinson!
When installing fresh power tubes, you have to remember that your old tubes likely required less negative bias to maintain the same idle current as they aged. Before plugging in your fresh set of power tubes, you may want to adjust the bias the so the reading on your meter is lower before plugging in the new tubes!
This is a very important step. If you have the bias setting turned up too high (technically the negative bias is too low, causing your meter to read a higher number), it may let the tubes get away from you once the amp is on. In some amps, this can result in a burnt fuse. or worse yet, a burnt resistor. If your amp uses a cathode or auto-biasing circuit, then you don't have to sweat this step, but if you adjust bias manually it is very important.
Upscale Audio includes matching of all its tubes, in any quantity needed, at no extra charge.
You cannot effectively match power tubes on a typical tube tester. Tube testers never applied the amount of voltage necessary to get accurate measurements of power tubes. In fact, there are only a couple very rare models that will allow you to get close to the voltages needed and allow you to read the parameters correctly. We use custom-built testing equipment that is the best in the business. We burn in and test power tubes at real voltages, and we test them for shorts, grid leakage, and excessive current draw before and after burn in to help minimize the chances of using your amp as a tube tester. Click here to read more about our test equipment.
Tube Life, noise, and do I leave the power on -
We get asked this question a lot. With a power amp, you would typically not leave it running 24 hrs a day. Power amps produce heat, and they use a lot of electricity. Preamps and source components that use small tubes are another matter. Regardless of what anyone tells you… I have not found a definitive answer to this question. I will tell you what I do, and you make a judgement call... remember... your mileage may vary!
Tubes age in a couple ways. One way is they lose emissions over their lifetime. Basically, they run out of gas. Tubes don't just "quit" suddenly. They lose their drive capability gradually with use. Small signal tubes like a 12AX7 or 6922 will work well on average for about 10,000 hours. If you leave your equipment on 24 hours a day, well you do the math: There are 8,760 hours in a year.
So when does a tube go bad? It depends on how picky you are. It's like a tube of toothpaste; Things kind of peter out at the end, but it seems you can always squeeze out a little more. Some products (and audiophiles) are pickier than others. I recommend to folks that want to upgrade to premium new old stock tubes that they do it while their stock tubes are good. That way you have the cheap ones working and available should you decide to sell the pre-amp.
The other way tubes age is they become noisy. Tube noise can present itself a number of ways. Sometimes the noise may sound like popcorn popping softly in the background, or it may become a loud roar. It can happen to any tube, including brand new ones. The most common reason that I have found for tubes becoming noisy is the coating on the filament becomes compromised. You can make the noise worse by turning your gear on and off a lot... that's the best way to guarantee trouble with tubes!
Usually, it's a good idea to leave your gear on during the day if you plan on listening to your system at different times, then turn it off at night. Of course it's always smart to turn your system off if you're leaving the house... whether it's for a couple of weeks or just a couple of hours.
Microphony, tube dampers, and tapping on tubes -
Okay...listen closely class, because I will say this only once: DO NOT TAP ON TUBES! You can permanently damage them! Repeatedly tapping on a tube's glass can cause a perfectly good tube to become too microphonic for use.
ALL tubes are microphonic to a greater or lesser degree. Whether or not that microphonics is audible will depend more on the tube's function in the product, rather than the microphony of the tube itself. In some positions, you will never hear anything, even with the worst tube. In other positions you will hear something even with the best tubes. At that point you make a judgement call: does this level of microphony interfere with my listening enjoyment?
Tubes are supposed to make noise when tap you tap on them! If a tube is truly microphonic, and in a position where it is critical, you will know it. It will feedback as you play music and be so objectionable you'll turn it off.
For those interested in a more in-depth discussion on microphony, click here.
Should I use tube dampers?
Uncle Kev doesn't care for them much, but... try them. Some folks like them. Others say tube dampers make the music sound sterile or hard. A small amount of microphony can be pleasing, as it can inject a sense of "air" into the presentation. This answer will vary based on the system, your taste, and the individual tube you are using. If you don't like the sound with the tube dampers, you can always take 'em off.
The 6DJ8/6922/7308 family of tubes is a special lot and are prone to be sensitive to vibration. That does not mean all of them are microphonic by definition; though some are. What's this mean for you? In high gain pre-amps, you may hear a slight "TING!" when flipping some switches. Usually this is caused by the grid wires picking up vibration through the tube pins. We listen to each tube in circuit and ship tubes according to the product it goes into, in order to give you the best results. If you own a preamp from Audible Illusions or CAT (to name a couple), and you experience a slight ring for a second when you bang on the pre-amp or flip switches, don't sweat it... unless you plan on playing bongos on your pre-amp while the music playing. I must say... if that's your plan... you may want to re-think your strategy.
One More helpful hint: We recommend that you have something hooked up to the output of any tube product when they are turned on. This applies to pre-amps, amps or anything else. If a tube preamp is left on for an extended period without being hooked up to a power amp, mute it.