The JJ EL-844 is a new version of the EL84 tube. It has Reduced power and a more balanced frequency response. Spiral Filament. It reduces headroom by approximately 25%, which allows it to achieve overdrive at lower volume levels.
The JJ EL844 has a maximum dissipation of 9 watts, as opposed to 12 watts of a standard EL84. The plate is physically smaller than the standard EL84. When using the JJ EL844 in and amplifier with fixed bias, bias should be set accordingly so the tubes at idle are between 50 - 70% of maximum dissipation.
When using the JJ EL844 in an amplifier with cathode bias, the bias resistor may need to be changed to keep the tubes from exceeding their 9 watt maximum dissipation.