JFET vs JFET equivalence

Thread Starter

spuddo

Joined May 2, 2013
58
I recently bought some Jfets (2N5565).
They are yet to arrive
I am hoping they will be good enough to do the job.
The circuit attached is the oscillator of a minimoog synthesizer.
In this schematic they show an E402.
An equivalents chart suggested an LS3954 or LS841.
In another article it was suggested that the 2N5565 could also be used.
I'm about to find out.
I believe the crucial thing is to match Vgs (cutoff voltage).

Could either of these be used in that circuit?

I have attached the data sheets of the LS841 and 2N5565.
Caveat: i'm a hobbiest not an EE.
Any thoughts.
 

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Last edited:

Ian0

Joined Aug 7, 2020
3,757
That's not going to be quite so critical as you have a matched pair. Matched pairs are used so that differences in Vgs cancel out.
 

Thread Starter

spuddo

Joined May 2, 2013
58
Hi Ian0 and MisterBill2 , thanks for your replies.
Attached is the data sheet for the E402 , as used in the audio oscillator cct.

I thought , that it was vital to have close Vgs figures for any replacement.

Vgs data:
2n5565 -0.5 to -3V
LS841 1 to 5V (? , why +ve)
E402 -0.5 to -2.5V

From this i guess the 2N5565 is closer to the original E402 and therefore the best replacement.
Please remember , i'm electronically challenged and my goal is to reproduce a vintage circuit as close to original as possible .
Any thoughts?
 

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MisterBill2

Joined Jan 23, 2018
9,809
It looks like your replacement will be better matched than the original, and the only issu that I see is the lower voltage rating. But since the circuit uses +10 AND -10 VOLTS it is not close to the 40 volt limit. So the challenge will be keeping the leads in the correct spots, and avoiding static electricity while handling the new parts. But there is lots of information available about that.
 

Thread Starter

spuddo

Joined May 2, 2013
58
It looks like your replacement will be better matched than the original, and the only issu that I see is the lower voltage rating. But since the circuit uses +10 AND -10 VOLTS it is not close to the 40 volt limit. So the challenge will be keeping the leads in the correct spots, and avoiding static electricity while handling the new parts. But there is lots of information available about that.
Thanks MB2 , hopefully the people who handled them before me were aware of this.
 
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