Sorry Damir, I have not gotten that far along yet. The real answer is, that I do not have a clue. I was hoping Douglas would be able to provide all of the necessary technical parameters. I am at the point of trying to figure out how much gain I will need. To include the sound character that I hope to accomplish overall. I would like to be capable of driving a three-way active system with an inpedance of around 50k and input sensitivity of 750mA. Any suggestions? I always try to reach for the golden ring before I have worked out all the details. I do know that less is best when it comes to gain strucure and components used in the signal path, everything has its own character to add to the mix. I see that Douglas has mentioned he is getting around 6db of gain in the Guinever when using the 12B4. Thanks Norris Wilson