JFET Testing Sanity Check

[Erik S]

I'm getting my parts together to build a Viceroy, and reading through @Chuck D. Bones development thread for that circuit:

Thread 'Monarch'

Dec 25, 2020

Here it is, the famous (infamous?) Monarch. Now that I have it working, I'm really liking this pedal. It's a great dirty boost that cleans up pretty well. Good control ranges.

Like many EQD pedals, this one requires mods to make it work right. The starting point is this schematic from Effects Layouts. Effects Layouts (Tangerine), Pedal Parts (Orange King) and Stewmac offer, or have offered Monarch kits. They all match the schematic below, except for one resistor value (R6). It's a simple design. 1st stage is basically a SHO. Next comes a James tone stack, followed by a gain...

• Chuck D. Bones
• Replies: 90
• Forum: Chucks Boneyard

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Chuck used PF5102 JFETs (Which I have, so far so good) and recommends something with a Vp no larger than 2V.
Following along in that thread, I pulled out a breadboard to build a test rig. (Figure 10 on this page):

A closer look at the Fetzer Valve

After testing my whole stash of ten PF5102s and looking at the datasheet, I realize that larger that 2v would be out of spec for a PF5102, and maybe none of this was necessary, but here's my dumb question:

Per the datasheet:

https://www.mouser.com/datasheet/2/149/pf5102-99964.pdf?srsltid=AfmBOor--xIPg1E-oBkTxJ_tdQNsbm5HrTQwggI8uR1jpzH9p5dg8Fym

Vp (Vgs off) for a PF5102 should be between -0.7 and -1.6

Idss should be between 4.0 and 20 mA


The values from my test rig appear to be in spec except that my Vp numbers are positive instead of negative.
Did I do something wrong, or is the polarity irrelevant?

 

[comradehoser]

My non-technical solution: could just socket the slots and audition what you have in there, since you already have a supply to choose from.

 

[Erik S]

My non-technical solution: could just socket the slots and audition what you have in there, since you already have a supply to choose from.

Yeah, I think I’m all set to move forward with the build using any of these, I was just trying to figure out if I did something wrong with the tester I built.

 

[darwin999]

@Erik S -
You are ok, the negative sign is often tossed.
E.g., see https://forum.pedalpcb.com/threads/...ve-with-some-mods-of-course.13466/post-318265

 

[Erik S]

@Erik S -
You are ok, the negative sign is often tossed.
E.g., see https://forum.pedalpcb.com/threads/...ve-with-some-mods-of-course.13466/post-318265

Thanks!