WHICH IS BETTER TRANSISTOR MJE340/350 OR BD139/BD140 - Page 2 - diyAudio
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Old 3rd September 2011, 08:11 AM   #11
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bd139 is better
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Old 3rd September 2011, 09:39 AM   #12
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Originally Posted by greierasul View Post
bd139 is better
Better for what? Are you suggesting BD139 is better in the higher power NMOS200 amp. as katiyar asks? Have you considered that an 80V transistor might fail as a VAS or buffer at the likely higher rail voltages? After all, there will be simple reasons to use a different transistor for a high power version but let's at least have the schematic or a link to it on this forum, to make assessments.

If you suggest BD139 is better in just the lower power amplifier, it could well be so, but that's not the question, as I read it. There are better transistors for either and both sizes or applications. Given that the BD139 has been around for at least 40 years, we could expect some developments, no?
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Old 3rd September 2011, 10:29 AM   #13
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Given that the BD139 has been around for at least 40 years, we could expect some developments, no?
Though it is a old workhourse it is actually an excellent transistor in all respects, keeping in mind its SOA.

This pair is nothing more or less than bc639/640 in a TO126 case for higher dissipation. If you look at datasheets for bc639 youll find that it is a very capable part. Because of the change to the TO126 case the cob will be slightly worse than for the to92 case so expect around 12-15pf. As drivers for outputstage working within their specified limits they are excellent, there are very few that equal its performance.
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Old 3rd September 2011, 10:55 AM   #14
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You could add a couple more repackagings for the old faithful BD139/40 over the years too. I believe the TO126 form was first by several years, as the TO92 form doesn't appear in my 1973 catalogue. It has been around, for sure and it's cheap and available everywhere too but I still want to know how a 200W/8 ohm MOSFET amplifier is going to utilise it.

Somehow, I just don't think so, in either VAS or say, Buffer role, do you?
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Old 3rd September 2011, 11:35 AM   #15
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Originally Posted by Ian Finch View Post
You could add a couple more repackagings for the old faithful BD139/40 over the years too. I believe the TO126 form was first by several years, as the TO92 form doesn't appear in my 1973 catalogue. It has been around, for sure and it's cheap and available everywhere too but I still want to know how a 200W/8 ohm MOSFET amplifier is going to utilise it.

Somehow, I just don't think so, in either VAS or say, Buffer role, do you?
Maybe, could be that the T0126 came first although I doudbt it as the service department tech at philips that gave me this info would have mentioned it, as I was also curious of this part, but it doesnt matter, what matters is that you can get all the datasheet parameters from bc639 like ft and cob figures and it is a very good part. A good question is if the manufacturers today like onsemi, SIT etc are keeping to spec regarding the originals as so far I see them all just copying the datasheets from each other.

I have to agree that I dont see it having any place on a 200w amp.
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Old 6th September 2011, 05:16 AM   #16
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Mje340 has ft=10Mhz and mje350 has ft=4Mhz. This is not too good for phase shift of the amplifier
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Old 6th September 2011, 01:29 PM   #17
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Any thought about MJE253/243 pair? In driver or VAS position...
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Old 6th September 2011, 03:13 PM   #18
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Any thought about MJE253/243 pair? In driver or VAS position...
They are good for driver, for optimum performance vas you should look at high voltage low cob types like 2sc1380, 2sc1381, 2sc1209.
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Old 6th September 2011, 04:31 PM   #19
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There is a search button on the front page which allows you to find threads full of posts about suitable transistors for anything in audio. Why not use them and learn a bit along the way? Just type VAS transistor (for example), select 'show threads' and read. - simple.

If you are trying to find suitable types in your region that may not be listed here, consider CRT TV driver transistors. These make excellent VAS transistors and some may even have sufficient peak current as MOSFET drivers too, since these do not require the heavy currents BJTs do. 2SC3503/A1381 are good examples as were BF469/70.
Note: as posted by Homemodder, low Cob, High voltage and Ft.
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Old 6th September 2011, 06:26 PM   #20
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It was a slight recommendation, my friend. It's Cob is really high a litle bit. Anyway, I used it as driver in a Sziklai pair. Tryed to compare with BD139/140, I couldn't hear/measure difference.

Last edited by megaymir; 6th September 2011 at 06:28 PM.
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