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I’m curious what it is about the 2N5485 N-channel JFET that makes it right for the Sabotage build. Are there other N-channel JFETs that substitute well? When I first saw the BOM for the Sabotage, I was unsure if my lysdexia had the better of me and wondered if they were actually 2N5458 N-channel JFETs that I mis-read.
I’ve compared the respective datasheets and they share same pin-out and each possesses identical “On” specs, but the “Off specs are different. The 2N5458 has a max Vgs(Off) of -7.0v while the 2N5485 has max Vgs(Off) of -5.0v. Also, the “Common Source Transfer Characteristics” curves are reversed between the two devices.
When the 2N5485 FETs arrive, I plane to curve-trace them and and compare those traces to those of the 2N5458.
I’ve also noted that the 2N5485 N-channel JFETs are now EOL – so going forward they may be difficult to find. In any case, I plan to socket them in my Sabotage build an swap between the 2N5458 and 2N5485 FETs and measure & listen to what happens.
Any good feedback will be appreciated.
The Sabotage first off is biased for using 2N5485. That would be the main thing since you know you can use many JFETs but biasing is not going to be the same as it is for J113, J201, 2N5457 or whatever. I have already verified that the Bias is best and set almost perfectly when using 2N5485 in the Sabotage circuit and since there are no trimmer adjustments well that makes them the best.
Barry – thanks for that. Good to know about availability. I did find my Sabotage PCB and the 2N5485 JFETs (and the BC550 that came with it when I bought the “deal” a while back.) I ran some traces curves and the average comparison values came out as seen in the attached image (screen-shots of the curve-tracing program that came with my Peak Atlas DCA75 test unit.) The curve traces suggest that biasing should be problem if swapping them out. Still, the acid test will be actually swapping them after I get it built. I’ll report back when I get that far.
The left column shows the 2N5458 JFETs and the right side column displays the 2N5485 test results.
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