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equvalent of MPS102 $ 2n5485

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ehsanjayjay

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HI all gurus
i search and find bf245c for mps102 but it have not in my country so can i use bf256 or bf247a instead mps102 and 2n5485????????:!:
thanks
 

lw1ecp

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Same procurement problems here in Argentina...
BF24* BF25* MPF102 2N3819 2N548* are very similar, seem to use the same chip. Differences among the members of a same family (e.g. BF244A B C; or 2N5484 5485 5486) are Idss (the Id for Vgs=0) and Vgs(cutoff). There can be an impressive parameters spread between different devices (e.g. Idss can be as low as 2mA or as high as 20mA) but many amplifier circuits can accomodate these variations by choosing the source resistor to get the desired Id. Hartley and Colpitts oscillators usually automatically adjust the gate bias. If in any doubt, please post your schematic and we'll see.
Please do not use J310 or U310 as substitutes, these are higher current parts.
 

ehsanjayjay

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HI thanks
i need this equivalen :
kt315
i use 2n3819 instead of mpf102 and bf256 instead of 2n5485 , but my circuit not work(sound my means),i ckeck and attantion to the legs(pin my mean)
cheers
 

lw1ecp

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Sorry, I can't find a datasheet for "kt315". Maybe there is a mistake in the code?. In case you read it on a real transistor, not in a schematic, please take into account most Japanese transistors omit the first characters, e.g. units beginning with "K" actually begin with "2SK". "2SK" means single gate JFET or MOSFET (dual gate MOSFETs are "3SK"). But after the "K" there must be a number, not an alphabetic character. Could it be your device is a "2SK1315" because the "T" was actually a "1"? This is a SMD power MOSFET. Could it be? Please post your schematic should you have it.
 

ehsanjayjay

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Hi
this is a Russion transistor.
what is the best aquivalent for MPF102 and 2N5485?them use in pi detector
cheers
 

lw1ecp

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ehsanjayjay, the old MPF102 is a very, very ambiguous part, the datasheet says Idss can be anything from 2 to 20mA, and expect any cutoff (pinchoff) voltage from about -0.5 to -8V, and transconductance from 2 to 7.5 millisiemens. Aghhhh!!! This is what one could call an out-of-control process. Nevertheless this is good news for you... *supposing* the original schematic would work with any MPF102, then almost anything can be used for substitution.
2N5485: I see this is more or less an intermediate between the BF244A and BF244B, different pinning. Can you get these?
BF247A: has Idss=30...80mA, much higher than MPF102's or 2N5485's, I DON'T recommend it as replacement.
BF256: the BF256B is more or less similar to the 2N5485.
But, what is the original transistor you need to replace: the MPF102, the 2N5485 or the KT315?.
Also, what is a "pi detector"?.
 

ehsanjayjay

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hi my friend .
many thanks
this name is baracuda detector and i need mpf102 & 2n5485?but they are not in my country.
i use 2n3819 instead all Mpf102 but the detector have not sound and i measure the frequncy and voltages and all is ok!!!so maybe these equivalent are not good.please help me
cheers and regards
 

lw1ecp

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Maybe the problem is not that you have used wrong equivalents. Sorry for my insistence, but we could probably be more helpful if you post the circuit. Don't you know how to do it?. Click Manage Attachments -> Add Files -> Basic Uploader -> Examine (there you navigate your PC to the desired file) -> Upload -> Done (I had never done this before, hahaha!, I have just attached two files trying to learn this).
Alternative: clic Add An Image -> click the English flag (unless you speak Polish) -> Select Files (navigate your PC) -> Upload -> manually copy the "BB Code" -> paste on the message
2147426300_1376698357.png
(and attached a 3rd file)
Having this info we could ask some questions on voltages, waveforms, etc.
 

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ehsanjayjay

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Hi my friend.
i really need your help.please
i put them for you.
thanks
list%20baracuda-%20components.jpgBarracuda_mod-bj-geotech.jpgIMG_0927-web.jpgIMG_0928-web.jpgIMG_0929-web.jpg
 

lw1ecp

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ehsanjayjay, I'm very sorry, I have just realized you had posted the schematics a long time ago.
I see the FETs are used as simple analog switches. There is nothing special with them. A funny thing in the hand drawn schematic is Q3=2N5485 and Q4=MPF102, why not the same type?
Looking at how Vss and Vdd for U1 are connected, I see Q3 or Q4's gate receives -5V when it is to be shut off, and 0V in the opposite state. Almost any JFET will obey this. If your system is not working, you can be sure it is not because of inadequate JFETs.
I hope this late answer can still be useful to you.
P.D. it seems incorrect that pull-up resistors on U1 are connected to "Vdd" line, they should go to ground, which is the Vdd for U1.
 

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