EML 300B mesh tubes
Warning for FAKE mesh tubes. More here....
Directly to the 300B mesh datasheets
EML 300BM+ - 300B-XLM - EML 300BM
General information about the use of mesh tubes.
The EML 300B Mesh is a wonderful and most amazing tube, which we have build for 25 years in unchanged version, called 300BM. This is not a regular 300B, but a long plate version, with higher heater current, larger outside dimensions, and reduced plate dissipation.
In the coarse of 2026, this 300BM will be replaced by the 300B-XLM, which is upwards compatible, and optically identical.
In addition, we now developed a 300B Mesh version which is directly compatible to the standard 300B tube. It is called 300BM+. It can directly replace 300B in any power amplifier. So to say, it is plug and play.
Emissionlabs 300B Mesh versions:
- 300BM. Classic low power version, made since 2001. Will be replaced mid 2026 by 300B-XLM, which is upwards compatible.
- 300BM+ The "plus" indicates it can be used in every 300B power amplifier.
- 300B-XLM. This is a mesh version of the 300B-XLS tube, where "M" means Mesh, and "S" means solid plate. Recommended for 300B amplifiers which can provide the higher heater current of 1.4...1.45 Ampere. Also 300B-XLM is upwards compatible to 300BM.
The trade off, between best sound and high output power
With every design, there is always the balance between best sound and highest output power. There is no way to get both out of the same tube, and 300B is no exception.
For this reason, some 300B amplifiers work at a lower output power, to provide more delicate sound for high efficiency speakers, head phones, pre amplifiers. Some other amplifiers produce the highest possible output power, touching the level where sound may become compromised.
All amplifiers, low power, medium power of high power, have a justification. This can be:
- A 'muscle' type of 300B amplifier. These give highest output power at the cost of other factors. Historically, this was the choice for Cinemas, and PA applications. Actually, the main application of 300B, at the time. Today, such are still the best choice for low efficiency speakers.
- A low power (7..9 Watt) or medium power (9..11 Watt) 300B amplifier, is what we see mostly, and when speaker efficiency matches to this, good triode sound will develop.
- A pre amplifier, or a driver stage with 300B, or head phone amplifier, is a very low power application. These give best possible sound, while output power is not important. Such applications, dealing with low signal, tend to be more microphonic. For this reason we recommend 300B solid plate for such amplifiers.
The speakers should match the amplifier
For very high efficiency speakers, it is wrong to operate those with a very powerful amplifier. This combination will give sterile sound, and noise problems. High power tube amplifiers by nature develop more noise, which noise however is a constant loudness, independent of the volume setting. This often will give a small background noise without music signal. This noise disappears if speaker efficiency becomes lower. So always try to combine a low power amplifier with high efficiency speakers, and vice versa.
Not just a noise problem, but also bad sound will also occur when an large output amplifier is combined with very high efficiency speakers. That is because tubes need to sweep through the curves enough to develop their characteristic sound. This means, a 50 Watt amplifier will never sound good at loudspeakers which need only 1 Watt. The amplifier will sound like a transistor amplifier. In the same way, a 6 Watt amplifier will not sound good at loudspeakers which need 5 Watt. This will lack dynamics, and bass will be muddy.
Please understand we build tubes, not amplifiers. Just we wish only, amplifiers and loudspeakers were better matched to each other.
Pre-amplifiers and head phones with 300B Mesh
This is not recommended, because mesh tubes, NOS or new made, have a higher noise level. Meaning not hum, but noise. If used as loudspeaker tubes, any noise will be not audible, but specially in head phone amplifier you may hear this. The problem is enlarged by putting the volume control not at the output, where it belongs, but at the input of the amplifier. We do not recommend mesh tubes for a head phone amplifier, or pre amplifier.
Biasing the 300B Mesh
Most normal 300B amplifiers run the tubes at a medium 30....36 Watt plate dissipation, resulting in 8...11 Watt output power.
There are a few kind of bias methods.
- Auto bias. WIth or without an indicating meter, there is nothing to change about it. 98% of the amplifiers is like this.
- Switchable Auto bias. With a switch, two or more operating points are possible. A very nice one is made by Trafomatic, Serbia.
- Adjustable Bias. These allow you to try out the difference between a low power and high power setting. These are a bit dangerous, because you can easily damage the tube with too high bias. These can be real tube destructors in the hands of amateurs..
- Mixed Bias. These are safe, but rare. You you can adjust the desired bias level, and it will be maintained in an auto bias way. Such are made by Mastersound, Italy.
- 300BM+ as a DRIVER tube. This is possible, it needs no further consideration, the tube is plug and play.
- Pre-amp tube. In that case, only 300B solid plate is recommended.
