All our preamp tubes are stringently tested for noise and microphonics using Amplitrex testers driving an external amp. There is no extra charge for low noise and microphonics testing like with other tube vendors. Additionally the tubes undergo a battery of tests for basic performance characteristics and faults such as: Emissions, Transconductance, H-K and Grid leakage, etc... If a tube does not pass our strict performance criteria it's tossed or sent back to JJ Electronic for evaluation.
Our "Balanced" selected 6SL7's are totally symmetrical in regards to plate current and transconductance. These are ideal for stereo applications where channel balance is critical. These can also be beneficial in driver stages such and long tail phase inverters.
If you need multiple matched tubes please see our "Balanced and Matched" option.