I'm finishing up a design here: https://123d.circuits.io/circuits/852190-jan-6418-vaccum-tube-valve-preamp which is a preamp for an instrument.
First, let me know if anything stupid pops out at you with this circuit, I'm not an EE :(
Second, the original design I'm modifying heavily is here:http://s13.postimg.org/patw5krxj/k270.png
Here is my current progress:
The original design calls for T1 to be a BSN254A, which is no longer available, so I need to concoct a replacement circuit. I think a mosfet was selected originally because it's voltage, not current, driven and doesn't put a load on V2.
I don't have the faintest clue how to select a proper replacement mosfet and how to calculate the values surrounding it. Where do I start?
Since this is a guitar stompbox project, supply voltage is 9v which is fed at v1 in the top right. My bad, I'll mark that on the schematic. Hoping to make this a PCB people will actually use to give themselves a nice warm tone with their guitars and mikes someday :)