The JJ ECC99 Gold Pin is based on the same construction as the original ECC99. The internal components go through additional selection and processing during assembly. After working with these tubes for several years we can confirm they do test more consistently and sound noticeably different than the standard ECC99. These tubes have a very lush and open character with an extended frequency response.
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. If a tube does not pass our strict performance criteria it's tossed or sent back to JJ Electronic for evaluation.