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PN 1855-0064

 

Looking for any info on this device. Dual JFET, N-channel, TO-71 package.? I have a 7652A and both were pulled from one of the boards.? I may pull one off another unit to curve trace but thought I ask if there's any spares out there first.??
 

1855-0064 isn't in the master reference list or the several cross reference lists I looked at. I found a hit on one of the NSN sites which isn't always reliable but this one shows the hallmark's of being correct.


This part number is not for a specific device. It describes a list of important specifications that are required.
Structure: multiple JFET transistors
Material: silicon
Polarity: N-Channel
Pd: 300 mW
IDss(Id when Vgs=0V): 1mA per transistor, 8mA all transistors
Case: 0.219in diameter, hermetically sealed?

Plugging those numbers in to I find 5 known part numbers that exceed those specs.
2N3921
2N3922
2SK146
IFN146
LSK389

Looking on Mouser it seems almost every modern dual JFET meets or exceeds those specs.

You will need to check the circuit to see what Vds and Vgs makes sense. The modern JFETs range form 10 to 60V for both.


On Sun, Mar 30, 2025, 5:12?AM John Warren via <johnwarren376=[email protected]> wrote:
Looking for any info on this device. Dual JFET, N-channel, TO-71 package.? I have a 7652A and both were pulled from one of the boards.? I may pull one off another unit to curve trace but thought I ask if there's any spares out there first.??
 

Took me a while to figure out why 7652A gave no results, a typo for the 7562A log voltmeter, the manual lists 1855-0064 as Siliconix DN643, which is also listed under the NSN number.
?
David
 

Thank you both for chiming in.??
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The unit is a 7562A, I apologize for the typo.
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I pulled a couple from another board and measured one side of each package, presumption is the other is similar.
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I was tweaking with the settings so some inconsistencies below.? ?The pinch off voltage range based on the two sets is between -1.6V and -2.2V.? IDSS 2.6 to 4.2mA at 10V VDS.
?
?
?
 

I'm not sure if you were asking if these meet the spec but I wanted to clarify how your finding verify the earlier numbers (for myself as much as future readers).

I believe the spec of Idss@Vgs0 is 1mA "or greater". The Drain-Source current when fully on (Vgs=0) is a primary characteristic of a JFET. Being able to pass more current than specified is OK. So an IDss of 2.5 or 4.2mA exceeds the minimum specification.


On Tue, Apr 1, 2025, 1:43?AM John Warren via <johnwarren376=[email protected]> wrote:
Thank you both for chiming in.??
?
The unit is a 7562A, I apologize for the typo.
?
I pulled a couple from another board and measured one side of each package, presumption is the other is similar.
?
I was tweaking with the settings so some inconsistencies below.? ?The pinch off voltage range based on the two sets is between -1.6V and -2.2V.? IDSS 2.6 to 4.2mA at 10V VDS.
?
?
?
 

Matched JFETs in TO-71, 6-pin packages are pricey.? Need to get a few with characteristics in the ballpark so I pulled a couple from a good meter and measured them.? ? ? ? ? ?
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