I bought two 6X-500 recently and i must admit i was very much impressed with the built quality and their sound, clean and slightly ballsy, the Pultec inspired EQ sounds great to, as they advertise, indeed very smooth HF. Perhaps the only issue with it is that a pop can be clearly heard when switching on and off the EQ, at first i thought it could be a fault but a very quick email reply from Lindell made it clear that it is something to do with the relation between the passive EQ and the high voltage opamp. A great pre and a great price!