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It can be quickly seen from the 300B working points at 250V / 60mA / 2700 Ohms, that the output power is approximately 0.6 Watt higher, and the distortion is 4dB less. We have to say, this is so at 2700 Ohms load, whereas the RCA 2A3 working point is at 2500 Ohms load. So loading the 300B-2.5V with 2500 Ohms vs 2700 Ohms, will further increase the output power to an estimated 4.2 Watt, at the price of perhaps 1.5dB more distortion. Yet, this leaves us with distortion figures, better than 2A3 still, and output power higher than 2A3. This is the idea behind the 300B-2.5Volt.
Bias Voltage at 60mA: It can be seen from the above tables, bias of the 300B25V differs 3 Volts from the 2A3. This is much within the natural tolerance of the 2A3. Though this was never officially specified, the bias voltage can well vary from -38V to -55V for some tubes.
If the increase in output power is indeed proven to work in any amplifier, we do not want to claim this here. It would mean improve such a great tube like RCA 2A3, simply by using the anode and the grid of the 300B. Yet, a compare of the electrical data as published by RCA and WE, does indicate this improvement clearly. From our side, we just would like to bring this tube under your attention as a possible and interesting replacement of the 2A3, with a sound character of it's own. It is expected to have slightly less distortion and slightly higher output power. We have to say also, we can not guarantee this to happen under all circumstances.
Some words about Distortion
In electronics, distortion can be expressed as percentage of the signal, or in dB. Using dB, is more related to human hearing, meaning a similar difference in dB, is experienced the same. This is why many technicians prefer dB. As as rule of thumb it can be said, a 3dB change can be heard by anyone, but below that needs a trained ear.
The 26dB rule of thumb: -26dB of 2nd harmonics is the level at which most human ears just do not hear this distortion. So at -25dB or more, you will experience this as minimal distortion. Whereas harmonics added with a levels of -20dB or more, sounds not pleasant any more.
Read More Here: http://www.emissionlabs.com/datasheets/EML300B-25V.htm