Setting up FET circuit.

[Dr d]

Hi all. Hoping everyone has had a good Xmas! Got a bit of free time and trying out an FET circuit for the first time. Are there any tips on how to set up (adjust) the circuit, please? Cheers.

[Dr d]

Anything at all would be most appreciated!!!

[martin manning]

It's a pretty simple circuit, but the way in which it is powered can have you chasing your tail. I found that powering it from a couple of 9V batteries (18V) before you connect it to the B+ is an easy way to find the source resistor value. Snap two batteries together and run a clip lead from "-" to ground and another from "+" to the top of the 10k drain resistor. This will give you a steady 18V Vcc. Find a source resistor value that results in drain voltage Vd of 9V (Vd = Vcc/2). For a new production 2N4416A, I am using 2.0k. For the voltage divider from B+5, the 150k series resistance shown in schematics is fine, but the shunt should be around 22k to get the correct Vcc (~20V). The thing is that the voltage dropped across the 150k (and therefore Vcc) is very sensitive to the FET's idle current, which will change as you are trying to get the Vd/Vcc relationship right.

[markr14850]

There are some discussions here:

https://tubeamparchive.com/viewtopic.php?t=10559

https://tubeamparchive.com/viewtopic.php?t=9561

--Mark

[Dr d]

A very big thank you guys for the input. This is a great help to me.