Please help to choose transistors from Mouser

[WLTerry]

Hey what's up

I'm about to buy a bunch of J201's from Mouser and there are three diffrent choices. Two of them seems to be the same thing put the 1st one is a bit diffrent:

Mouser Part #	Idss
512-J201	80 mA
512-J201D27Z	0.2 mA to 1 mA
512-J201_D74Z	0.2 mA to 1 mA

Also I want to buy 2N5457's and there are diffrent choices, for example:

Mouser Part #	Idss
512-2N5457_D27Z	1 mA to 5 mA
512-2N5457	2.5 mA to 5 mA
863-2N5457	1 mA to -5 mA

And some BS170's, they have different Forward Transconductance and Resistance Drain-Source

I want those trannies to build FET-based overdrive/distrotion valve emulators and boosters. So, do you know which of those trannies would be my best choices? What characteristics should I need to look at?

Any help will be welcome. Thanks.

[brett]

Hi
in my experience, there are only a couple things to consider.  I'm no expert, but I've messed with FETs a bit.
 
In general a J201 will be specified wherever high transconductance is needed (e.g. high gain in a simple common source amplifier).  A 2N5457 is specified for lower transconductance.  For many circuits, any J201 and any 2N5457 will give good results.

Within each type of device, high transconductance is associated with high Vgs(off) (ie less negative.  -2V out-transconducts -3V), so if you wish you can buld a JFET tester (geofex.com) and sort them.

For the BS170 you'll usually want low "on" resistance and high transconductance, so check the spec sheets for those data.

Unfortunately, for FETs and MOSFETs, there'll always be a wide range around the nominated values, so don't necessarily expect to get devices that match the specs.  Many people buy a few extra devices and sort through for the ones that sound best.
cheers

[ubersam]

Hey what's up

I'm about to buy a bunch of J201's from Mouser and there are three diffrent choices. Two of them seems to be the same thing put the 1st one is a bit diffrent:

Mouser Part #	Idss
512-J201	80 mA
512-J201D27Z	0.2 mA to 1 mA
512-J201_D74Z	0.2 mA to 1 mA

Those suffixes just indicate the packaging type, Tape and Reel option and Ammo Pack option. The transistors are the same J201 as 512-J201, except 512-J201 comes in single pieces, no tape and reel, no ammo pack.

Also I want to buy 2N5457's and there are diffrent choices, for example:

Mouser Part #	Idss
512-2N5457_D27Z	1 mA to 5 mA

Same deal here.

512-2N5457	2.5 mA to 5 mA
863-2N5457	1 mA to -5 mA

512-2N5457 is by Fairchild, 863-2N5457 is by ON Semiconductor. Either one should be fine, but I'd get the Fairchild for no reason other than that is what I have been using.

[WLTerry]

Thanks guys.... I'll check those specs. Something new I learn every day