WHICH IS BETTER TRANSISTOR MJE340/350 OR BD139/BD140 - diyAudio
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Old 2nd September 2011, 03:47 AM   #1
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Default WHICH IS BETTER TRANSISTOR MJE340/350 OR BD139/BD140

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.
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Old 2nd September 2011, 04:41 AM   #2
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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

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Last edited by wintermute; 2nd September 2011 at 04:55 AM. Reason: add comment about current.
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Old 2nd September 2011, 09:43 AM   #3
jaycee is offline jaycee  United Kingdom
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Better for what exactly?
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Old 2nd September 2011, 09:59 AM   #4
AndrewT is offline AndrewT  Scotland
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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.
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Old 2nd September 2011, 12:28 PM   #5
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I suppose the question should be which one makes the best driver for an output transistor.
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Old 2nd September 2011, 03:07 PM   #6
artu is offline artu  Chile
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Quote:
Originally Posted by AndrewT View Post
To me, when I read the datasheets, they are completely different transistors.
I would never consider one to be the equivalent of the other.
....
I did it once and got oscillation

Cheers
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Old 2nd September 2011, 06:18 PM   #7
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The NMOS200 amplifier Schematic uses BD139/BD140 whereas NMOS350 amplifier Schematic with higher voltage uses MJE340/MJE350.
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Old 2nd September 2011, 11:05 PM   #8
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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).
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Old 2nd September 2011, 11:24 PM   #9
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Originally Posted by artu View Post
I did it once and got oscillation

Cheers
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.
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Old 3rd September 2011, 07:33 AM   #10
CBS240 is offline CBS240  United States
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Quote:
Originally Posted by katiyar View Post
The NMOS200 amplifier Schematic uses BD139/BD140 whereas NMOS350 amplifier Schematic with higher voltage uses MJE340/MJE350.
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.
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