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Old 22nd Apr 2021, 1:35 pm   #19
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: Tektronix P6201 FET Probe repair

I can do some more tests this evening but the Idss for the 2N4416A I have here was measured at 5Vds and it was 8.36mA. The Vp was -3.2V for <1uA Id.

The bias tee resistance used in the source was 2177 ohm.

I try and include as much info in my S2p files as possible in the filename as below and this can be quite useful if a more detailed analysis is required.

2N4416A(CG(5VDS(1MA(VP3200MV(VGS2170MV(IDSS8360UA. S2P

A quick play with an old excel design spreadsheet predicts that with 8.36mA Idss and Vp -3.2V the source resistor for 1mA bias should be 2093R so this 2N4416A JFET is working quite close to theory as I used 2177R for 1mA. See the screenshot below.

That datasheet for the die has a 2N5485 listed and this is a classic 'middle of the road for Idss' process 50 JFET.
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Regards, Jeremy G0HZU
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