Ruby Tubes EL84CZ-2 are the most powerful EL84. Much like the GE6BQ5.Great compromise between tone and reliability. Nice mids, sparkling highs and solid bottom end. They can take the heat and vibration in stride without any negative tonal effects.A premium tube that produces more power, more tone, and higher fidelity with an extended dynamic range. All Ruby output tubes are labeled on the base with the exact matching measurements for plate current and transconductance. By matching these parameters, optimal performance and long life are ensured.The Ruby Tube EL84CZ-2 matched output tube is sold in matched duets. The Ruby EL84CZ is the strongest EL84 output tube being manufactured today. The EL84 duets have been tested and matched for output power, stability, plate current and microphonics.All Ruby Tubes carry a 6 month warranty period against manufacturers defects.All Ruby Tubes power tubes come already matched. There is no extra charge for this service. The matching process is very exact and our tubes are matched within +/- 1 mA (mille amp) of each other.The EL84 CZ-2 delivers superior performance in demanding conditions such as class A guitar amplification.