Can BD139/BD140 be safely replaced with high voltage transistors MJE340/MJE350 without change in circuit parameters. Will there be any change in performance of the circuit in respect of audio performance & distortion etc.
I'm not a good person to answer, but I think that knowing the application would help people to answer 🙂 These could potentially be used for both VAS and Drivers depending on the amp.
edit: a quick look at the datasheets shows BD139 1.5A collector current, MJE340 0.5A collector current. whether or not that is relevant though depends on the application 😉
Tony.
edit: a quick look at the datasheets shows BD139 1.5A collector current, MJE340 0.5A collector current. whether or not that is relevant though depends on the application 😉
Tony.
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To me, when I read the datasheets, they are completely different transistors.
I would never consider one to be the equivalent of the other.
If they are not equivalent then there is no sensible way to assess whether one is better or worse.
Accept that bd139 are low voltage, high current, medium power devices
and MJE340 are high voltage, low current, medium power devices.
I would never consider one to be the equivalent of the other.
If they are not equivalent then there is no sensible way to assess whether one is better or worse.
Accept that bd139 are low voltage, high current, medium power devices
and MJE340 are high voltage, low current, medium power devices.
The NMOS200 amplifier Schematic uses BD139/BD140 whereas NMOS350 amplifier Schematic with higher voltage uses MJE340/MJE350.
It depends on the current you want to drive. BD139/BD140 are rated at (at least on the original Philips data sheet) 80V Vceo and 100V Vcbo/Vcer. Not all manufacturers keep to the 100V Vcer, but in principle you should be able to use the BD139/BD140 at up to 70W from +/- 45V rails. They typically have a current gain of 100 at 150 mA and a minimum of 63 (originally 40), and work well up to 250 mA hence are good drivers for 2N3055/MJ2955 pairs.
The MJE340/350 are primarily high voltage transistors. They have a low fT (around 20 MHz, but this is not specified on the data sheet) and poor current handling (typically rated at 50 mA). SO it depends what you want to use them for. Why not use 2SC4793/2SA1837 for a decent high voltage driver? THey are high voltage high frequency drivers and work well at over 200 mA, so they are like a good extension of BD139/BD140 for higher powers than 70W (i.e. 100W or more).
The MJE340/350 are primarily high voltage transistors. They have a low fT (around 20 MHz, but this is not specified on the data sheet) and poor current handling (typically rated at 50 mA). SO it depends what you want to use them for. Why not use 2SC4793/2SA1837 for a decent high voltage driver? THey are high voltage high frequency drivers and work well at over 200 mA, so they are like a good extension of BD139/BD140 for higher powers than 70W (i.e. 100W or more).
If used in the VAS then a capacitor is required from c to b. I found 220pf to be a good compremise.
The same capacitor is needed from c to b if used as a quasi lower driver.
This is irrelevant. What is the purpose of the devices within the circuit? This is where you would determine the operating region of the transistor and thus if it will fit or not. Other things may also come into play, Ccb and a couple other parameters...... maybe not.😕
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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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.
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?
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.
Mje340 has ft=10Mhz and mje350 has ft=4Mhz. This is not too good for phase shift of the amplifier
They are good for driver, for optimum performance vas you should look at high voltage low cob types like 2sc1380, 2sc1381, 2sc1209.
SEARCH
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.
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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