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Anyone have luck finding a drop in replacement for the 2sk139 and 2sj49 mosfets? I had one of these years ago and replaced these same parts, but I am having trouble finding replacements now.
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Oh geez, those things were selling for like $20 each 20 years ago, so good luck. I am one very fortunate man, I have a dead four channel power amp that someone declined the estimate on some time ago. The four power amp channels were those things in push pull. So that dead carcass of an amp has 8 of them. At one every few years, I figure that will cover me the rest of my professional life. But no, I don;t want to sell them. Not meaning to tease.
We have covered this before, but since I have my secret stash, I never paid a lot of attention. Seems to me folks were stuffing some TO247s into the socket holes. No TO3s around, not at reasonable cost anyway. You might search the forum here for just the part number.Education is what you're left with after you have forgotten what you have learned. -
2SK139=NTE 2397
2SJ49= NTE 2998
Ah, thank you very much...Comment
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Avoid NTE parts, if at all possible.
Expensive (that would be the least problem), but often only "somewhat" approximate to the part you really need.
The favorite choice of lazy technicians who just want to send the amp through the front door and cash that bill as soon as possible.
If you can't find the originals, this is the real deal ; they even have improved "2 dies in a single case" versions.
Those would be the 16A, 250W ones.
Lateral Mosfet
Good luck.Juan Manuel FaheyComment
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There is nothing wrong with nte parts, they work fine.
The people who bash nte are the ones who don't know how to troubleshoot, and they blame their lack of knowledge and failure on the parts.
Too bad, they always work fine for me.Comment
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Excuse me, I think I know damned well how to troubleshoot, thank you very much, I have been at it for over 50 years. Longer than NTE has been around I might add. And Mr Fahey is no inexperienced tech either, his credentials are considerable, as not only a repair tech, but also a designer and commercial manufacturer of amplifiers.
I highly recommend staying away from NTE parts, in particular parts used with other parts in power amps. If you replace say an MJ15003 in a row of same in some power amp with an NTE sub, the NTE part will NOT be an MJ15003 in spec or performance. It will be something NTE feels is EQUIVALENT enough to work in its place. Unfortunately that is no guarantee the parts will share current well at all. That can result in the NTE part turning on a little sooner thanthe rest, and thus "hogging" current, or it can result in the NTE part turning on a little later, leaving the rest of the parts to carry the load, essentially, the NTE part disappears.
The problem is that inexperienced repair techs assume the NTE parts are the exact same thing they are replacing, and they are not.
NTE2397 comes up as a TO220 part, not the TO3 we need here. The NTE 2998 shows NTE2906 as its complement.
Another problem with the NTE line is the cost. For example, the MJ15003 is $3.50 at Mouser. The NTE sub, NTE60, sells for $10.20. 2N4401, 2N3904, 2N5088 sell for 6, 7, and 8 cents each at Mouser. NTE crosses all three of those, and hundreds more, to the NTE123AP, which sells for $1.25.Education is what you're left with after you have forgotten what you have learned.Comment
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+1 on the new two-die mosfets, they do a good job in those mosfet Trace Elliot bass amps.Originally posted by J M Fahey View PostComment
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I just saw an amp I repaired 24 years ago, a Randall Switchmaster.
I put NTE transistors in the preamp 24 years ago, and the transistors are still working just fine, today.
Which just goes to show you, when applied correctly, there is nothing wrong with NTE parts, they last just as long as the original, or longer.
People who badmouth these parts are blaming the parts for their own inability to fix the equipment, and lack of knowledge to apply the parts correctly.
It's easy to blame the parts for your own failure. But fixing equipment the right way? That takes skill, no matter what type of parts you buy.Comment
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Well, the problem is exactly that, applying them correctly, since their actual parameters match expected ones seemingly at random.Which just goes to show you, when applied correctly, there is nothing wrong with NTE parts, they last just as long as the original, or longer.
Of course, if you actually measure them, and use them accordingly, you will have no special problems.
In the example mentioned above, NTE suggested a plastic TO220 transistor instead of a metallic TO3 one.
No problem, if you use it where a TO220 one will be enough ... not to mention that you'll have to kludge a different mounting system, bend the legs awkwardly .... and pay more than the correct part price to boot.
Now, if the original amp was not that much overbuilt, and really needed a metallic TO3 there ... may the Force help you.
Agree, people without much skill or experience blindly use these parts, either on their own or following some gurus, and then say "it must have been a bad part" .... which, among other factors, might be true.People who badmouth these parts are blaming the parts for their own inability to fix the equipment, and lack of knowledge to apply the parts correctly.
Agree.It's easy to blame the parts for your own failure. But fixing equipment the right way? That takes skill, no matter what type of parts you buy.
As you see, I agree a lot with you
As of the preamp example you mention,
1) it's agreed by most of us here, that practically *any* TO92, 25V , beta>100 small signal transistor can be used *anywhere* in a preamp or similar small signal circuit , with no reliability issues.
Respected Elektor magazine even suggests using generic transistors in their projects, wherever applicable.
So, TUN mean "Transistor Universal NPN" , TUP same in PNP, DUS is the equivalent general purpose small diode, and so on.
So in that case it would have been difficult for NTE to *miss* that one.
2) As said above, small signal processing is light duty.
Very much doubt a poorly specified *Power* transistor, specially in an unforgiving guitar amp will perform reliably.
jm2cJuan Manuel FaheyComment
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Have you guys bought off that profusion site safely? When I go through the checkout it asks me for some bank password stuff, and my internet security starts going off. Is there another place to get those? I did some searching and couldn't find any dealers who have them.Comment
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They do not sell to the public, only to Manufacturers, Distributors, Shops, Government and similar customers.
That's why they ask for all kinds of info and background before even quoting.
Email them and ask them for some retailer or distributor who sells to the general public.
I guess they will suggest some UK company like Maplin, Farnells or similar, but they *should* have some US representative.
Post what you find, it will be interesting.
As you can see their login page is an HTTPS secure page, not a run of the mill one.
This is just one I found:
A&J AUDIO TORQUAYS ONLY ELECTRONIC COMPONENTS AND SPARES STOCKISTS
As a local example, I can get them in Buenos Aires, for a good price , about 1 hour from my home:
BAGUI S.A. coolers, turbinas, baterķas, semiconductores, cabezas de cd, transformadores, fuentes y mas
as a reference, their list price is: http://www.bagui.com.ar/pdf/762.pdf
so, by definition, it *should* be easier on the US .
Juan Manuel FaheyComment
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Replacement lateral MOSFETs can be purchased from profusionplc (and they sell to public - at least they were few months ago). Or you may buy BUZ901/906 - slightly more expensive from Farnell. I used 2SK1058/2SJ162 in similar amp but they are in different package. They are cheap but they are slightly less powerful - I got 180W from 2 pairs in a bass amp. And they need an adjustment of the bias voltage.
MarkComment
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I replaced the rectifier diodes, disconnected the mosfets and discovered the PT is shorted.
Where can I find a replacement? The schematic I have just has the part #, I don't know what the specs are.Comment
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Any 36+36VAC : 150VA or more (up to 250VA) transformer will do nicely.
Primary voltage to suit your Country, of course.
The original one was a classic EI type, today you might find a toroidal.
Will do, if it fits.
Mounting is different though.Juan Manuel FaheyComment
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Thats 36 volts center tapped?Comment
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