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Dead JFETs?


bhjazz

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I have a pair of 2n5457/5458 JFETs on a small board as part of a bias scheme for a 12AX7.  The circuit also has a 9v battery.  I cannot get the voltage dialed down, so I checked the JFETs.  The resistance from gate to source (and gate to drain) read the same in both directions: roughly 1k ohm.  These are dead, aren't they?

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If you are measuring out of circuit (so there is no confusion with any other parts on the board) then they are dead.  Gate to drain or source is diode-like.  Depending on the JFET, drain to source will be tens to hundreds of ohms either way around with the gate open.

Possibly a turn-on transient while the tube warms up has killed them?  Without seeing the schematic it is kind of difficult to tell for sure.

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Craig, thanks for the confirmation.  I appreciate it.  They are currently in-circuit, so that could mean they are storing a charge somewhere and staying open.  I had suspected the diode-like properties had gone away, which prompted my post.  I'll remove them from the circuit for testing and if they are, indeed, burned out, I would have to replace them anyway.  

Thanks again.  

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