300B-25-Mesh Data Sheet


2A3 Mesh tube

Warning: This tube can not be used in a classical 300B amplifier. For testing with a tube tester, you need to use 2A3 settings

The EML 300B-25 is a direct replacement for the 2A3 tube.

High Resolution

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The first owner can register the tube within 4 weeks after receival, at the Emission Labs ® website, to participate in the 5 years guarantee program, which is additional to the legal obligations of the seller.

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This is a 300B-Mesh with the heater of the 2A3.

Sound Character of the EML 300B2.5V

Users of 2A3 tubes, so far have a limited choice of tubes to use. There was only 2A3 and 2A3-Mesh. With the 300B25 we offer an alternative tube. The idea is to get a slightly different sound, and possible a small gain in output power for any amplifier.

It is interesting to see, electrical data of the 300B tube at the operating point of 2A3 is very similar, and apart from the heater voltage, a 300B could replace the 2A3. So we have put the heater of the 2A3 tube inside a 300B, to get a 300B tube with heater specifications of the 2A3. We have called this tube 300B25 ('25' stands for 2.5V heater).

The above table shows three working points from the 1930's Western Electric 300B data sheet. The last working point shows 250V, 60mA, -45V bias. This is identical to the 2A3 tube. This means the tube will bias normally in any 2A3 auto bias circuit. Yet dynamic parameters are slightly different, which indicates sound will be slightly different as well. Due to the somewhat higher load (2A3 is loaded with 2k5 normally, vs. 2k7 required here for the 300B) the output power may be slightly increased accordingly. Also it can be seen, the 300B works in a range with the lowest distortion here, 30dB 2nd harmonics and even 45 dB 3rd, harmonics. Such good numbers can also be expected from the 300B-25.

Filament Ratings (See note 5)
Filament Voltage
2.5Volt (AC or DC)
Tolerance on filament voltage
2.4 ... 2.6V at Tube pins
2.5 ... 2.7V at Socket pins
See also the Note about Heater Voltage
Filament Current


All other Data
See 300B Mesh



Heater Voltage: Some people experiment with lower filament voltage, to expect better lifetime. This is essentially wrong to do. If the magic was that easy, we would make the tubes like this ourselves. Under Heating can lead to early loss of emission, though new EML tubes will fully recover once the heater voltage is corrected, older tubes will recover only partially. The specified filament voltage at 0% tolerance is the one for best lifetime. The voltage we specify, is at the TUBE PINS itself. Any voltage drop by the socket contacts must be compensated for. For 2A3 tubes, some sockets have 50mV voltage drop per pin, because the heater current of 2.5 Ampere is very high. Causing a total drop of 0.1V for both pins together. So a voltage of 2.6Volts at the socket pins is needed, to make sure there is 2.5 Volts at the tube pins.