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. (You are already here)
Amplifiers which need special attention
Introduction.
Actually, problems with Emission Labs tubes are rare. When replacing tubes, most users 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. When it works they say: The tubes are good quality because they work well after many years". Or, at a problem, the they say: "The tubes we bought, were not good, because they failed too early".
Then, at a problem 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'. Well at that moment, yes. If both tubes are mistreated, there is no rule saying, they must get equally bad at the some moment. Likely one gets bad first. So you can plug the bad tube from the one channel to the other, or in another amplifier, and of course 'problem follows the tube'. What does this tell you? Well me it tells only, one tube works, and the other not.
Really, you are so much better off, first read the documentation before servicing a tube amplifier.
Luckily, such amplifiers exist, where you can blindly replace tubes indeed, and these are ideal products of course. But, before you think yours is like that, better look that up in the manual. Some 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 amplifiers by post, every normal person will try to avoid it like monkey plague. But often this situation is provoked, by keeping documentation 'secret'. This is a trap for buyers of new equipment. When the day comes you need service information, they may not give it. So I recommend always, DO NOT buy an without service documentation and the schematic.
Yet, it is a repeating problem, when no repair person can find be found near by, what shall the poor owner do?! Some amplifiers weigh 20kg or more, and need dedicated shipment crates, to send then to the other end of the world. So, people try to do the exchange themself. Carefully plug the new tubes in, and hey.... it WORKS. Then, the crying becomes loud when a tube gets defective half a year later. Some users require free replacements, but then it becomes really strange, if they have the only intention to repeat the failure they made before. Meaning again they will blindly replace the tube.
Please take the above with a grain of salt, but is does reflect the things we see. Try the following: Operate two light bulbs at 10% too high voltage, it will work very satisfactory for quite some time, and you think you did it right. Then one will fail without warning. So you can swap the broken lamp in the other sockets, to confirm it the problem follows the lamp. But what will that tell you about the cause? Nothing! Also guess what happens if the seller replaces the lamps for you? The will break down again, of course!
Most errors occur in this order:
- Emission problems, due to wrong heater voltage
- Thermal overload of the whole tube
- Spark effects inside, due to in-rush current out of specification
In the following pages, we want to give some background about how to prevent problems, by correct installation.
With power tubes, such as EML builds, any complication is loss of good function. 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. He was never interested in the mains voltage, Why should he? So 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, some just do it. 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.