JFET identification

Yeah, it's tough trying to match up a JET if the pin off voltage is a critical part of the circuit. Also on top of that, it could be used as a current source which makes it just as tricky.

I recently repaired a analog PID board that another tech repaired in the past. They replaced the JFET switch that is in the output that effectively turns the PID loop on/off. The way it is set in there, the gate pinch off voltage must fall in the range of 1 to 5 volts(-) and the tech put a NTExxx replacement in. That was a bad call. The NTE replacement had a gate pinch off voltage of 5..10V-. This circuit only had -5 max to play with. Needless to say, it wouldn't switch properly

50% of the time. so wee went shopping for the original replacement, TO-92 package. guess what, I couldn't find any but I did find one that had the Gate voltage that I needed and the Idss was even better than the original.. So we go those. They are like gold these days!

One friendly warning, beware of using NTE parts in critical areas. They don't always work.

Jamie

Thanks for that. I think I'll try giving Keithley a call, maybe I'll get lucky...

Or not. They'll sell me the $2 part, but with a $150 minimum. They claim this part is made to Keithley spec (!). They also offered the following info:

"I also show that we purchased these (which were not made to KI spec) Interfet SJN132280 Fairchild Semiconductor 5149B51374A Fairchild Semiconductor 5149_NB51374B"

I was unable to find any datasheets or stock on any of them. *sigh*

More than likely a standard fet in fairchild list of JFETS with a custom number on it for them. This is done very often to force you to use their service centers or to force you to buy new from them. However, buying new would mean they have a good product! :)

THe last company I can remember that made custom things for their products were people like Tektronics and I know there are a slew of others that do that for undisclosed customers.

If you had a schematic with voltages and basic functions as to what it does, it would be easy to come up with a replacement.

Jamie

Wild guess

Interfet IF1320?

JC