[sdiy] Substitute for IMF-3958 ARP 4015 S/H SubModule

[Roy J. Tellason]

On Wednesday 28 May 2008 08:55, Csaba Zvekan wrote:
> Hi everybody,
>
> I am looking for the IMF-3958 or 2N3958 N-Channel J-FET for a ARP 4015
> S/H Submodule (ARP2600). Is there a good substitute ?

I'm thinking "E402" comes to mind for some reason -- dunno if that was a part 
that Moog used or what.  It's not that critical,  and pretty much any dual 
FET should work for you in that application.  Perhaps the charts I have 
online would be of some help with that:

http://www.classiccmp.org/rtellason/parts-index.html

> Also looking at the schematics from ARP-TECH's site. I don't understand what
> the "GUARD" means coming from the Source of the 2N4392 to the two Gates of
> the 2N3958. 

That refers to specific traces on the board that are designed to be at or near 
the gate potential.  As high impedance as that circuit is,  the layout of the 
board is fairly critical,  as well as things like cleaning it off of flux 
after you've soldered the new part in,  etc. -- you'll notice they don't use 
any solder mask on there,  or any other kind of coating,  they told me it 
caused them problems.  Just don't mess up the traces while you're removing 
and replacing and make it a point to clean things up afterwards and you 
shouldn't have any problem.

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