My purpose is not to dissuade DIYers from building the F5 or any other amp or preamp that uses the Toshiba JFets. BUT, there is a very real problem sourcing these devices at this point in time.
Bogus devices, ones that are jfets but not ones that meet the curves or specs of the Toshiba are being sold from a variety of sources. This includes some "name brand" distributors, apparently.
An amp like the F5 will certainly function, produce sound with these devices, but it won't really meet specs. A big issue is that the devices that are marked as 2SK170 and 2SJ74 that are being sold are *not* complimentary. It would be better if using other jfets that they be complimentary in this circuit.
I am not sure, but thinking back, retrospectively, this alone may account for some of the very wide variations in reported sonics for the F5.
there is a discussion that includes these parts here:
http://www.diyaudio.com/forums/parts/82638-my-transistors-original-copy-10.html
This is a real problem, and I thought it important enough to start this thread.
Bogus devices, ones that are jfets but not ones that meet the curves or specs of the Toshiba are being sold from a variety of sources. This includes some "name brand" distributors, apparently.
An amp like the F5 will certainly function, produce sound with these devices, but it won't really meet specs. A big issue is that the devices that are marked as 2SK170 and 2SJ74 that are being sold are *not* complimentary. It would be better if using other jfets that they be complimentary in this circuit.
I am not sure, but thinking back, retrospectively, this alone may account for some of the very wide variations in reported sonics for the F5.
there is a discussion that includes these parts here:
http://www.diyaudio.com/forums/parts/82638-my-transistors-original-copy-10.html
This is a real problem, and I thought it important enough to start this thread.