Has anyone thought of building their own tube preamp? Anyone who was around in the 1960's remembers the Knight kits and the Heathkits...and also learned something along the way.

I haven't used a Hamptone pre, but I understand that is available in kit form. There are probably other ones out there as well. The D.W. Fearn preamp is a good one and it is built in PA, near Philadelphia.

If you decide to "roll your own", the usual preamp tubes such as the EF86 (6267), ECC83 (12AX7), ECC81 (12AT7), ECC82 (12AU7), and the 5879 can still be found. I don't advise going to a tube manual and building a mic preamp using their schematic for professional work. I would suggest looking up preamp schematics from old consoles or commercial equipment for a start.

If you are adventuresome and want to design your own, some of the more "esoteric" tubes such as the D3A or the 417A would be a good start for the input stage, with a high quality mic input transformer (Jensen, Sowter, etc.). The power supply is just as important as the preamp. The first gain stage is the most important. Any noise here follows the rest of the way (one reason for using a well shielded mic input transformer, noiseless 15 to 20 db gain). DC filament heating is mandatory, and the HT must be well filtered and preferably regulated. The DC HT supply required is on the order of 300 volts, and be careful when working around the HT. The filter caps can hold a dangerous charge even with the unit turned off.