Good day.
I have not been on the forum for a long time.
I have 2 old quasi complementary amps that is using 2n3055 on the output. about 5 years ago I swopped the 3055;s with 2N2773
I was wondering if I can replace the 2N3773 with Darlington transistors like MJ11015?
I am running a 300VA transformer one each amp at 56v. I use them directly inside a 15inch speaker.
My thinking is that currently I run 4 2N3773 Transistors. If I place the Darlington's in it will be like I have 8 transistors.( or not) Will I be able to push more current to the speakers ??
Please tell me science on why this will work or not work.
I have not been on the forum for a long time.
I have 2 old quasi complementary amps that is using 2n3055 on the output. about 5 years ago I swopped the 3055;s with 2N2773
I was wondering if I can replace the 2N3773 with Darlington transistors like MJ11015?
I am running a 300VA transformer one each amp at 56v. I use them directly inside a 15inch speaker.
My thinking is that currently I run 4 2N3773 Transistors. If I place the Darlington's in it will be like I have 8 transistors.( or not) Will I be able to push more current to the speakers ??
Please tell me science on why this will work or not work.
It doesn't quite work like that 🙂
The Darlington is an arrangement of two transistors to make what appears as a single transistor with extremely high gain. Also the MJ11015 is a PNP device wheras the 2N devices you mention are NPN.
There are other considerations as well such as the higher turn on voltage as you now have two effectively series connected base/emitter junctions.
So the simple answer is no, its not a good idea and it doesn't do quite what you imagined it might.
The Darlington is an arrangement of two transistors to make what appears as a single transistor with extremely high gain. Also the MJ11015 is a PNP device wheras the 2N devices you mention are NPN.
There are other considerations as well such as the higher turn on voltage as you now have two effectively series connected base/emitter junctions.
So the simple answer is no, its not a good idea and it doesn't do quite what you imagined it might.
A Darlington has no more power handling ability than a BJT. It is a combined driver and output transistor, which is useful in some cases but usually suffers badly from miller effect limitations because the driver emitter-output base is not accessible outside the device. A primary cause of BJT amplifier failure is shoot-through current due to a week pull-off drive to the output transistors. A Darlington has two diode drops between the base and emitter, which is generally incompatible with circuits designed for a BJT. So Darlingtons have lots of gain but they are slow, ie. a bad choice for amplifiers that operate above 1KHz.
2n3773 are great rugged old NPNs that cover a multitude of sins. You might consider replacing half of them with 2N6609 PNP power transistors but that would require changing the circuit from quasi-complimentary to complimentary. You could then use cross-coupling to improve the high frequency behavior, and odds are the rest of the circuit could use some updates. I would simulate any changes in LTSPice, including the stability and effectiveness of current limiting, overdrive behavior etc. But mostly as a learning exercise that doesn't blow up expensive parts.
I wouldn't do that nowadays. Unless you have some trusted NOS laying around you won't find any real 2N6609's. If you wanted to do this, use MJ15004. It is a close cousin of the 6609, and for practical purposes in an amplifier just as good. Rated SOA at high voltage is lower, but at practical rail voltages for a 140V device it is good enough.
If you really want to push more current with the amp, you need to parallel up more outputs. If you kept the same protection circuitry it would limit at about 2x where it does now. And if you're not hard limiting, higher currents would still be easier because the output transistor gain would hold up better with half the current thru each device. If you do this, make sure parallel pairs (triples, quads, etc) are matched at least for vbe. Same lot is usiually good enough. You may double up the old ones and add a pair of new, for instance.
If you really want to push more current with the amp, you need to parallel up more outputs. If you kept the same protection circuitry it would limit at about 2x where it does now. And if you're not hard limiting, higher currents would still be easier because the output transistor gain would hold up better with half the current thru each device. If you do this, make sure parallel pairs (triples, quads, etc) are matched at least for vbe. Same lot is usiually good enough. You may double up the old ones and add a pair of new, for instance.
Hi there.
Thanks for the prompt replies.
I don't have a circuit diagram and will have to strip the speakers to redraw the circuit.
This is just something I was contemplating while lying awake 2 o'clock in the morning.
I made a small typing error. I was referring to the MJ11016 which is an NPN Darlington.
Well I guess I must stop dreaming up stuff in the early mornings.
Thanks for the prompt replies.
I don't have a circuit diagram and will have to strip the speakers to redraw the circuit.
This is just something I was contemplating while lying awake 2 o'clock in the morning.
I made a small typing error. I was referring to the MJ11016 which is an NPN Darlington.
Well I guess I must stop dreaming up stuff in the early mornings.
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I disagree. My TGM6 amplifier uses complementary Sanken Darlington transistors at the output. They are very fast devices. The amplifier works very well indeed. It is based on a modified commercial amplifier, which uses many of these Sanken Darlingtons and is sold at very high volume (home theatre).
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