Some information about the 300B Mesh tube.
the EML 300B Mesh is a wonderful and most amazing tube. The use of this tube requires some care, because it is no plug & play replacement for any 300B. However excellent sound quality is possible with this tube.
Some 300B amplifiers work at a low, quite delicate operating point. Some work at an average operating point, and some others try to get the highest possible output power. Obviously, as the above three methods are all used, each has it's own justification. We do need to understand what that justification is, so what did the designer have in mind when he build this amplifier. With amplifier design, there is always the trade off between best sound, and highest output power. It's not possible to have best sound, and highest output power in one design.
We really need to look at how the amplifier design is presented. When we have a "muscle" type of 300B amplifier, claiming to get so and so many Watt out of a standard 300B tube, it has to be clear, the design compromise here was: power at the cost of sound quality. By the same idea we have to understand amplifiers which can produce medium output power only, and such which produce only low power. (of course a pre amplifier, or a driver stage with 300B is also a low power application)
Important is, that speakers should be balanced with the amplifier.
Meaning, if you have speakers with very high efficiency, it is not ideal to operate those with a "muscle" kind of 300B amplifier. It's high output power is not needed, but at the same time, such an amplifier sounds a bit sterile or dominant at very low power. So to say the triode sound is not really there, because it develops only when there is more output signal on the tube, which characterizes such kind of an amplifier. Such speakers benefit a lot more from a typical low output power 300B amplifier.
However when speaker efficiency is low, any low power type of 300B amplifier would be forced to run at it's maximum. Even though with a low power amplifier, distortion at the same output power is much lower, you may find the volume dissatisfactory if combined with low efficiency speakers. In such a case you would operate the amplifier rather at the end of it's capabilities, and dynamics of the output signal may suffer.
Please understand we build only the tubes, but the EML 300B-Mesh, which we talk about here, is designed to use in 300B amplifiers of low and medium-low output power only. So it can not be used in any 300B amplifiers with very high output power. (For this, consider plain EML 300B or EML 300B-XLS)
We can not go into more details here about the nature of triode sound, so what is the physical reason behind this much sought after, sweet, silky triode sound. We can say, the best way to achieve this sound, is bias the 300B tube at medium Anode dissipation. (so not at the highest possible). Of course this will give less output power, compared to what is possible at a maximum. So you need to know for yourself, if this lower output suits your needs still.
The finest and sweetest sound has always been produced by the smaller size tubes. To get enough loudness, use speakers chassis with strongest magnets, and you need just a few Watt. In this light the EML 300B-Mesh has to be seen. It is a tube for listeners that can do with somewhat less loudness, but for that seek more triode-like sound, with the magic and transparency of the wire mesh Anode tubes. If this is what you want, we recommend EML 300B-Mesh.
To replace a 300B by the EML 300B-Mesh, be sure the wire mesh tube is run at following conditions:
Recommended: 22Wat Anode dissipation.
Absolute maximum 28 Watt Anode dissipation.
This is 70% of what is done with standard 300B in most of the cases. Though this is sure not always so. Some 300B amplifiers are made for medium or even low power by default.
A conservative 300B amplifier runs at 26....36 Watt. Without measurement, you can not know where are on this scale. So suppose it was 26Watt or even less, you could plug&play the EML 300B-Mesh. On the other hand, it it was 36Watt, you would damage the EML 300B-Mesh by just plugging it in. So this is going to need good attention.
Basically there are three kind of Amplifiers:
When you intend to do the exchange yourself, but have no idea what the above means, do not do it yourself. Have a good techincian do it. Do not randomly experiment with the 300B mesh, since there is no guarantee on a burned out tube. The best is use plain EML 300B in that case. Or use the EML 300B-XLS, which is a plug and play upgrade tube for the standard 300B.
Here is a good hint when you need to modify the amplifier to use 300B mesh. Just do the modification, by using the standard 300B at first. Then when it works, do it once more with the 300B mesh, and you work a lot safer that way.
In case you have the sound you were looking for, after replacing the 300B by EML 300B-Mesh, but you feel you need a fraction more loudness, the most advised solution is to use loudspeakers with higher efficiency, not use tubes that can be driven harder.
Well... you made it until here...