The combination of tubes and amplifier needs always some attention

Part 1. What to do in problem cases.

Part 2. Amplifiers which need special attention

Abstract

Actually, problems with Emission Labs tubes are very rare. For the few cases we had, it seemed seldom a direct quality problem of the tubes, or the amplifier itself, but more a problem of the way the combination, or the tubes were replaced. However if any defects occur, it is likely a problem with the tube heater voltage, or users replacing tubes in amplifiers, which need adjustment after a replacement. Likely with too low heater voltage, such problems will disappear after correct adjustment. Yet with too high bias, or too high heater voltage, initially everything seems to work fine, and any problems if they occur later, can not be solved any more.

If any problem occurs, it can be one of those:
  1. Emission problems, due to wrong heater voltage
  2. Spark effects inside, due to in-rush current too high
  3. Loss of power output, due to thermal overload of the anode
  4. Spark effects inside, due to in-rush current too high

In the following pages, we want to gives some background about how to prevent problems, by correct installation.

In problems were we are involved, it is usually those, where tubes develop a problem after relatively short time. In such cases, we must find the root cause. The reason is very simple: Replacing tubes which were damaged by wrong use, will only repeat the problem. Even when the problem is in the amplifier, sometimes tube replacement can solve it. Yet, it should be clear, without knowing the root cause, the problem is not solved at all. The problem it just not visible. Strictly speaking, the problem with the amplifier becomes already visible, because it will not work well on random good tubes, but only on particular tubes.

We do not build ECC83 tubes at EML, so we give neutrally this example: Some amplifiers are build with this tube at a position in the circuit, where signal is extremely low. Any tube, no matter what age or brand, will show some noise, but with good circuitry, this can be prevented. Though this is difficult. The art of analog design, is not getting hum an noise, by working with the components that you have. True art like this, will result in totally noise free and hum free products, without being pickery on the brand or the selection. If the designer fails to do so, logically the user will observe some noise or hum. Then like always, this will be dependant on the brand and the selection. What else do you expect?! Still some amplifiers play totally hum free and noise free, on any pair of random tubes. So if you remove this "noisy" ECC83 from amplifier Brand-A and put it in amplifier Brand-B, and the noise is gone, this shows which of the two amplifiers is better designed.

With power tubes, such as EML builds, any complications is rather loss of function, and once the tube has stopped working, the root cause can not be found easily. Yet if the root cause is indeed the amplifier, replacing the tubes will only repeat the problem. Even so, replace the tubes may seem to solve such a problem, though of course amplifier problems are not solved that way, just become not visible.

For instance, somebody has broken tubes in a 220V amplifier, which was connected to 240V mains, and he did now know this, and never look at the mains voltage, because there never was a problem. Until he replaced the tubes. Logically he will say, 220V or 240V, was never a problem, so why is it now?

When we analyze this, it means he expects tubes to work fine in a 220V amplifier, which he connects to 240V. He feels this should be possible because it never went wrong. At this moment, already the conclusion is wrong. The users says it never went wrong, but it fact it did go wrong, because that is what we were talking about.

In short, users expect from the tube Lifetime and Quality. If plug&play appears to be possible, does not mean this was a right thing to do. You would find out only after a defect, but it is too late then.

These pages just try to give some assistance. Good users manuals are rare. So at EML we try to help you out, when manufacturers play a hide and seek game with manuals, but it is assistance only. We do not have responsibility for the amplifiers.