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.
When you have a "muscle" type of 300B amplifier, claiming to get so and so many Watt out of a standard 300B tube, sometimes you are dissatisfied with the sound, being somewhat dominant, and you don't experience the triode sound you have been looking for. Getting best triode sound out of a 300B doesn't mean to choose the highest possible operating point, and get an amplifier on steroids. Loudness should not be produced by inefficient speakers which have to be "kicked" with high amounts of energy. Without going into the details of this, it feels already obvious that the much sought, swee, silky triode sound, can not be achieved, by an amplifier firing the 300B close to the breakdown point.
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 300B-mesh has to be seen. It is a tube for listeners that can do with a fraction less loudness, but for that seek more triode-like sound, with the magic and transparency of the mesh plate tubes.
If you want to replace a 300B by the 300B-mesh, be sure the mesh tube is run at following conditions:
Absolute maximum 28 Watt.
This is 70% of normal. 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 300B-mesh. On the other hand, it it was 36Watt, you would damage the 300B-mesh by just plugging it in. So this is going to need some attention.
Basically there are three kind of Amplifiers:
- Auto bias. To use the 300B-mesh, you need to know how to check the setting, and how to reduce it to 22...28 Watt. This is a standard job for a good technician, it needs no further explanation.
- Adjustable bias. To use 300B-Mesh here, simply adjust for 22Watt. Since adjustable bias is less stabile and precise than Auto bias, it is not recommended to go much above 22 Watt. Some manufacturers have a meter in the amplifier, which provides a number. They just say "set it in 20" or whatever the number is. In such a case reduce the setting of the 300B-mesh to 70% of the value which the manufacturer advised for plain 300B. So instead of "20", take "14". Or when "80" is a normal number, take "56". Etc.
- Combined construction. For the end user, these amplifiers behave like the Adjustable bias amplifiers. They need less often an adjustment than pure adjustable amplifiers.
When you intend to do the exchange yourself, but have no idea what the above means, or there is no technician to do this for you, we recommend not to 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.
In case you have the sound you were looking for, after replacing the 300B by 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.
Serious warning for FAKE mesh tubes. Read more here
Continue HERE for the data sheet of the only real 300B-MESH
300B Mesh Data Sheet