Replacing tubes needs often special attention. The combination of some specific designs, and users which are not qualified to service amplifiers, causes problems.

Contents

Introduction.

What to do in problem cases.

Amplifiers which need special attention

Introduction.

Actually, problems with Emission Labs tubes are very rare. When replacing tubes, many users carefully read the amplifier manual, and instructions which are with the new EML tubes, and ask when they are not sure what to do. But, unfortunately, also some users just replace the tubes blindly, and when it sounds good, or better than before, it's fine for them. Their expectation is, a replacement is ok, as long as the sound is good. Then, at a problem, the complaint is about tube quality, because the sound was good after the replacement, or even before, and the new, expensive tubes appear to have broke down without reason. Then comes the usual swapping of the bad tube, from the left to the right channel, and this seems to verify the cause is 'the tube'.

Really, you are so much better off, first read the documentation before servicing a tube amplifier. If experienced service men do this, it's not without reason.

Luckily, many such amplifiers exist, where you can blindly replace tubes, and these are ideal products of course. But, look that up in the manual, before you do so. Many other amplifiers are simply not like this. Manufacturers have sometimes the standpoint, users must send in or bring their amplifiers for a tube exchange. Needless to say, shipping tube the amplifier by post, every normal person will try to avoid it.

Yet, when no repair person can find be found near by, what shall the owner do?! Some amplifiers weigh 40kg, and need dedicated shipment crates. So, people try the exchange themself. Then, the crying becomes loud when a tube gets defective half a year later. Some require free replacements, but then it becomes really strange, if they have the only intention to repeat what they have been doing before.

Please take the above with a grain of salt, but is does reflect the things we see. The conclusion is mostly like this: If defects occur, it was often a problem with the voltage or current at some point. Like when operating two light bulbs at 10% too high voltage, it will work very satisfactory for quite some time, and then one will fail without warning. So you can swap the bulb in the other sockets, to confirm it was 'the bulb'. But what will that say? Not much.

Most errors occur in this order:

  1. Emission problems, due to wrong heater voltage
  2. Thermal overload of the whole tube
  3. Spark effects inside, due to in-rush current too high, by wrong design

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

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!!

For instance, somebody has broken tubes in a 220V amplifier, which was connected to 230V mains, and he did now know this was important. In fact not know it at all, because there never was a problem. Until he replaced the tubes. Logically he will say, 220V or 230V, 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 230V. 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 a blind replacement appears to be possible, does not mean this was a good 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 the usual a hide and seek game with manuals, but it is assistance only. We do not have responsibility for the amplifiers, and if they let you down with 'secret' schematics, that's what they are doing, they let you down. Please note, in Europe anyone who sells products over here, is obligated by law to supply whatever information it needs, to perform a repair. So secret tools, secret schematics, unavailable instructions? It's illegal behavior. This must be supplied, at no more then self cost.

Part 1. What to do in problem cases.

Part 2. Amplifiers which need special attention