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This powerful triode is designed for amplifiers without compromise. This tube is not directly in the family of 300B tubes, but closely related. In few words, it is made for somewhat higher voltage, and it has somewhat higher gain.
The higher gain has a practical reason. The amplifier designer (or the ready amplifier) may already have a good working 300B drive circuit. Due to it's higher gain, the 1605 will produce the higher output signal, at the same input signal as a normal 300B driver stage will deliver. (This is maximum 60 Volt AC)
The higher output power is achieved by the higher Anode voltage, keeping the Anode current at the same level of tubes like 300B-XLS or 520B. The transformer manufacturer can easily make a good SE transformer for higher voltage, but has problems with much higher DC current. For this reason we have chosen the 1605 to be a somewhat higher voltage tube. Like this, it can be used with normally available SE transformers. All in all, this will make it convenient to make a new design with the 1605, which is inspired by existing 300B amplifiers. Finally, the lower bias voltage of the 1605 will help to make the power supply more efficient in case of auto bias amplifiers.
Even amplifiers that are designed for the 520B-V3 can be adapted for the 1605 in many cases with only minor changes. Provided the amplifier has enough Anode voltage of appr 580V, all you need is adapt the tube bias, and check if the heater current can be supplied.
The high filament current, stands for excellent emission, which on a glance can be recognized by the beautiful linearity of the tube curves. On the long term, high filament current is the source for higher tube life as well
Read More Here: http://www.emissionlabs.com/datasheets/EML1605.htm