This may be a stupid question but I've used the search feature for awhile looking for a layout of something that will allow me to test the particular bias resistor needed for my fet's off board that way when I solder them into place I don't require sockets or trimmers for biasing
I'm wondering if the answer to your question is simply a solderless breadboard. Good way to test out and tweak just about anything before soldering.
Quote from: EBK on March 20, 2017, 11:55:36 AM
I'm wondering if the answer to your question is simply a solderless breadboard. Good way to test out and tweak just about anything before soldering.
+1
Just build up the stage on the breadboard, dial it in, then transfer the parts to your PCB for soldering.
$4.95 for this small one - great for quick testing little things.
https://www.sparkfun.com/products/12002
(https://cdn.sparkfun.com//assets/parts/8/5/0/3/12002-04.jpg)
I was going to suggest building a JFET tester to determine Idss and Vp for your specific part, but Jubal81 is right. Just get a small breadboard and test it there. Shouldn't take too long to find a resistor which biases you JFET. Make sure to label the parts so there's no mix up later when you solder them in ! ::)
pogo pins
Quote from: R.G. on March 22, 2017, 07:17:23 PM
pogo pins
R.G., I fear that you are being a bit too cryptic (for me, at least). I know what pogo pins
are, but just what are you suggesting that our dear doctor should
do with them? :icon_confused:
Quote from: R.G. on March 22, 2017, 07:17:23 PM
pogo pins
I searched - still no idea what or how.
Quote from: duck_arse on March 23, 2017, 09:59:51 AM
Quote from: R.G. on March 22, 2017, 07:17:23 PM
pogo pins
I searched - still no idea what or how.
This. (https://en.wikipedia.org/wiki/Pogo_pin) (Hadn't heard of it either... Perhaps I ought to have done: I worked for Cray in a previous life.)
Yes, yes, but I'm still unable to see the connection (no pun intended). Please enlighten me. What do pogo pins have to do with this?
Quotelooking for a layout of something that will allow me to test the particular bias resistor needed for my fet's off board that way when I solder them into place I don't require sockets or trimmers for biasing
Quote from: Doctor Algernop on March 20, 2017, 10:08:37 AM
This may be a stupid question but I've used the search feature for awhile looking for a layout of something that will allow me to test the particular bias resistor needed for my fet's off board that way when I solder them into place I don't require sockets or trimmers for biasing
Solderable male nail pin connectors..!!
(there aren't neither sockets nor trimmers..) :icon_wink:
Quote from: antonis on March 24, 2017, 07:32:11 AM
Quote from: Doctor Algernop on March 20, 2017, 10:08:37 AM
This may be a stupid question but I've used the search feature for awhile looking for a layout of something that will allow me to test the particular bias resistor needed for my fet's off board that way when I solder them into place I don't require sockets or trimmers for biasing
Solderable male nail pin connectors..!!
(there aren't neither sockets nor trimmers..) :icon_wink:
That's what I was thinking too. It meets the negative requirements, but so does a water balloon.
Risk management for accidents due to loose parts in relation with conductivity leads to use of water balloons...
Back to the OPs question, if you're talking about a "standard" common source JFET gain stage, you can calculate the bias and required resistors pretty accurately (I have a spreadsheet which does this), BUT you need to know the actual Idss and Vp for your JFET. Given the wide range of Idss and Vp variation for a given type like a J201, there is no substitute for measuring. You can build a simple JFET tester pretty easily (for example, http://tagboardeffects.blogspot.com/2012/07/greatly-improved-jfet-matcher.html (http://tagboardeffects.blogspot.com/2012/07/greatly-improved-jfet-matcher.html)), and test all your JFETs and organize them in individual plastic bags with their Idss and Vp recorded. Yeah, it's a bit of work, but...
If you don't like all of this fussing around, then use op amps... :icon_biggrin: