For this article let's accept an axiom that warming up heaters well before raising B+ is a must for any good behaving thermionic valves based equipment.
At a first glance there's nothing difficult in building a unity-gain preamp: the well known and fairly simple source follower should do the job. However in my case it turned out to be quite an adventure. Why "HotFET" - please refer to this article.
|HotFET-Pre (c) - prototyped in a "networking" case|
The design is pretty simplistic. There were many calculations, tests and Continue reading