J174 replacement part

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Dyonight

Well-known member
Joined
Feb 18, 2014
Messages
90
Hi!

I just got a Marshall JMP-1 preamp replacement board that seem to have been bumped while handled and I spotted a Jfet (I think) which legs have been broken.

Since it's an NOS board, the part is obviously discontinued and I can't find any information about it anywhere.

The numbers on it goes as follow:

J174
F0552AB

I'll add a pic as well.

Anyone can recommend a good quatily part that's easy to source that would make a good replacement?

Thanks!
 

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Oh wow first time I get an answer that presume I'm an idiot that can't use google, thanks, I guess.

I found a ton of J174 but they all have different characteristics regarding voltages and prices varies a lot so there have to be a difference. I can't just throw the cheapest thing that says J174 on the package, can I?

I could not find any infos about this specific one, which number is F0552AB, so I don't know what the operating voltage should be, if it matter, or any rule of thumb that could help me get a suitable one, etc. I'm not a jfet expert and don't wish to spend the next month becoming one for this specific repair.

With this in mind,  thanks to help me with that.
 
Would the InterFET one in the 2nd link you provided be a suitable replacement?  If yes how are you able to determine this?

Thanks
 
Dyonight said:
Oh wow first time I get an answer that presume I'm an idiot that can't use google, thanks, I guess.

I found a ton of J174 but they all have different characteristics regarding voltages and prices varies a lot so there have to be a difference. I can't just throw the cheapest thing that says J174 on the package, can I?

I could not find any infos about this specific one, which number is F0552AB, so I don't know what the operating voltage should be, if it matter, or any rule of thumb that could help me get a suitable one, etc. I'm not a jfet expert and don't wish to spend the next month becoming one for this specific repair.

With this in mind,  thanks to help me with that.

I wasn't trying to insult sorry. I just wasn't sure if you did the google search first. 
F0552AB is most likely manufacturing code, as to when and batch number it was made.

At work we use a couple jfets, order by the thousands and match them which takes days so that we get what we are looking for.  I think you would be find with whatever j174 you put in there as currently you have no target spec you are looking for.
 
Ok no problems I understand some people don't bother doing some basic searches before posting here!

Indeed I don't know how to find those specs so I'll try something from a reputable manufacturer and hopefully it will do the job just fine.

Thanks for your time!
 
Dyonight said:
Ok no problems I understand some people don't bother doing some basic searches before posting here!

Indeed I don't know how to find those specs so

go to any reputable parts seller (like digikey)
https://www.digikey.com/product-detail/en/fairchild-on-semiconductor/J174/J174FS-ND/1050079
then click on link labelled datasheets
https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/J17x,MMBFJ17x.pdf

sometimes the links won't be fully labelled as data sheets but there will be a red and white PDF icon, click on that.
I'll try something from a reputable manufacturer and hopefully it will do the job just fine.
As far as what specs the Marshall JMP-1 needs, maybe ask Marshall
Thanks for your time!

Many people that post answers here are busy so won't be very touchy feely...  Pucho's answer was just matter of fact. If that bothers you just wait...  ;D



JR
 
Help us to help you -

- Find a schematic
- Post it to the thread
- Save us time by showing us where your specific broken part is on the schematic, I see three on page 1 alone.
- This will allow people to determine whether the component specs are critical (like the front end of a discrete opamp) or non critical (FETs used as switches for example).

That said I would be straightening out those legs and using the part I had if at all possible.  Simple JFET performance tests are outlined here - https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/


 
Thank you all for the schematics and the advices,  I'll be able to search for the right info and my next post will be done the right way.
 
JohnRoberts said:
Many people that post answers here are busy so won't be very touchy feely...  Pucho's answer was just matter of fact. If that bothers you just wait...  ;D

Yes no problems with waiting and I understand it takes time to answer and even search for infos to help someone here, that's what I meant by "thanks for your time". Did it sound like I was impatient? I'm french so I may not always understand the exact meaning of what I'm saying :)
 
Dyonight said:
Yes no problems with waiting and I understand it takes time to answer and even search for infos to help someone here, that's what I meant by "thanks for your time". Did it sound like I was impatient? I'm french so I may not always understand the exact meaning of what I'm saying :)
No, I meant if that bothers you just wait, because something more offensive can come along later.  ::) 

I was trying to be funny, but perhaps it didn't translate.

JR
 
JohnRoberts said:
No, I meant if that bothers you just wait, because something more offensive can come along later.  ::) 

I was trying to be funny, but perhaps it didn't translate.

JR

Ah ok got it! Ouch I feel like I have problems to follow I'll take a break ahah!
 
Marshall used these P JFETs as simple switches. ON/OFF, no "sonic mojo" here.

J174 with legs is getting scarce but not that hard to find a few of.
 
Alright!

First thanks for all your answers!

The transistor that was broken is TR15.

On the board, it is physically situated close to the input jack, phone jack and output level pot.

The unit power on as expected and the output signal is quite sufficient.

Any idea what this part is used for?
 

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Here's where it is supposed to go, in case that could help
 

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when TR15 is turned off, it is a high impedance or open circuit. When turned on it is a low impedance and connects R193 to C12, effectively putting R193 in parallel with R192 for lower resistance. In that circuit the gain of that stage is 1+R191/R193&R192.

I don't know if that schematic is accurate but it looks like the outputs of two opamps may be shorted together. Never a good thing, but schematics are often inaccurate.

If it was working before put a good J174 in the old hole. I wouldn't worry too much about the specs.

JR
 

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