I want to use either a 2N3055/MJ2955 or TIP41/TIP42 pair for a class B amplifier project. I know the 2N3055 is an old design so, I'm worried about switching speed/slew rate, but it can handle about 2x the power of TIPs. What do you guys think?
Why not use some decent transistors?
Check the thread about Digi-Key stocking the
nice Toshiba Power transistors. About $2 ea.
The problem with the 3055s is that you could
expect to find most anything inside of them as
they were so loosely spec'ed. I don't know
if they still exist, but the Motorola/ON MJE2955/3055
was a better choice since you at least got the same
die inside the package each time you purchased.
Check the thread about Digi-Key stocking the
nice Toshiba Power transistors. About $2 ea.
The problem with the 3055s is that you could
expect to find most anything inside of them as
they were so loosely spec'ed. I don't know
if they still exist, but the Motorola/ON MJE2955/3055
was a better choice since you at least got the same
die inside the package each time you purchased.
Why aren't the TIP's "decent" for power amps? What exactly makes a transistor good or bad besides power handling?
Many of those transistors are manufactured with much liberty from their specifications. With better transistors come tighter specifications and more reliable characteristics in a working atmosphere.
Well, decent "bandwidth" , aka Ft.
Flat Hfe vs Ic
Breakdown voltage 2X the absolute max rail-rail supply voltage (1.5X absolute min)
High enough current rating
High enough power rating
Sufficient Safe Operating Area
(for the above 3, don't forget to consider real loads with complex impedances vs. freq, not just an 8 Ohm resistor)
Low thermal resistance from junction to case.
Check the other threads on the newer Toshiba and On Semi output transistors
Download the datasheet for these newer devices and then compare to the datasheets for the TIP41/2 (Fairchild has a datasheet)
Note the TIP41 costs $0.86 from Digi-Key; the Toshiba devices $2.25. Skip a couple trips to McDonalds or Starbucks and
buy better transistors.
Flat Hfe vs Ic
Breakdown voltage 2X the absolute max rail-rail supply voltage (1.5X absolute min)
High enough current rating
High enough power rating
Sufficient Safe Operating Area
(for the above 3, don't forget to consider real loads with complex impedances vs. freq, not just an 8 Ohm resistor)
Low thermal resistance from junction to case.
Check the other threads on the newer Toshiba and On Semi output transistors
Download the datasheet for these newer devices and then compare to the datasheets for the TIP41/2 (Fairchild has a datasheet)
Note the TIP41 costs $0.86 from Digi-Key; the Toshiba devices $2.25. Skip a couple trips to McDonalds or Starbucks and
buy better transistors.
OK, I see the Toshibas have an Ft well in the 40mhz range. From what I understand, this is the frequency where common emitter gain is equal to 1. The TIP41/42 has an Ft of 3Mhz, well outside of the audio frequency range. Is this because the response starts to fall off well before 3Mhz? The price isn't deterring me, if I use TIPs I will use many of them. Could someone please provide me with a part number (NPN/PNP) for the Toshibas so I can look them up?
The TIP looks only a bit better, but if you are looking for something in a TO220 or TO126 package, look up the 2SA1186 or 2SA1941 and their compliments. There are probably newr and better than these, but they both look a bit better on paper than the two you mention.
Can you tell me why they look better than the TIPs? Assume that I can use multiple TIPs to make up for lower power ratings.
"Can you tell me why they look better than the TIPs? Assume that I can use multiple TIPs to make up for lower power ratings."
Basically it is the Ft spec. Although anything in the Mhz range would seem unrelated to the audio spectrum, higher Ft seems to relate to lower base-output capacitance for similar power/voltage/current parts. So why is lower base-output capacitance good? In a class B amp each transistor in a pair shuts off for half a cycle (an over-simplification but ok for this explanation). When this happens there is a spike or "blip" emited by the transistor. Keep in mind the the base-collector side of a transistor is kind of like a diode. Ordinary recifier diodes exhibit this behavior as well when they shut off. I don't know whether this is truly a case of "capacitance" or not, but it is certainly capacitor-like. Anyway, this turns out to be one of the more significant contributions to noise in a bipolar transistor. The size of the bip is less at lower capacitance (higer Ft), thus less noise.
I don't know if I've explaned this quite right, but if not hopefully someone will correct me.
Basically it is the Ft spec. Although anything in the Mhz range would seem unrelated to the audio spectrum, higher Ft seems to relate to lower base-output capacitance for similar power/voltage/current parts. So why is lower base-output capacitance good? In a class B amp each transistor in a pair shuts off for half a cycle (an over-simplification but ok for this explanation). When this happens there is a spike or "blip" emited by the transistor. Keep in mind the the base-collector side of a transistor is kind of like a diode. Ordinary recifier diodes exhibit this behavior as well when they shut off. I don't know whether this is truly a case of "capacitance" or not, but it is certainly capacitor-like. Anyway, this turns out to be one of the more significant contributions to noise in a bipolar transistor. The size of the bip is less at lower capacitance (higer Ft), thus less noise.
I don't know if I've explaned this quite right, but if not hopefully someone will correct me.
Mr. Snake,
Please look at the recent threads on Toshiba and ON Semi power
transistors for more information and part numbers. That's
why this site has a search engine.
Then I'd suggest reading some basic college Sophomore/Junior
electronics textbooks to find out about transistor basics.
Try "Electronic Circuits, Discrete and Integrated" by Schilling
and Belove. If you can find it, read "Intuitive IC Electronics"
by Thomas Fredericksen for a good intro to transistors.
Then you can read the stuff about amplifier design on Douglas
Self's web site and/or buy his Audio Power Amplifier Design
Handbook. In fact Mr. Self devotes most of a chapter to
showing why modern transistors like the Toshibas are better
than his old favorites (MJ802/4502, which themselves are
much better than 2N3055/2955 or TIP41/42).
Seek and you will find.
Please look at the recent threads on Toshiba and ON Semi power
transistors for more information and part numbers. That's
why this site has a search engine.
Then I'd suggest reading some basic college Sophomore/Junior
electronics textbooks to find out about transistor basics.
Try "Electronic Circuits, Discrete and Integrated" by Schilling
and Belove. If you can find it, read "Intuitive IC Electronics"
by Thomas Fredericksen for a good intro to transistors.
Then you can read the stuff about amplifier design on Douglas
Self's web site and/or buy his Audio Power Amplifier Design
Handbook. In fact Mr. Self devotes most of a chapter to
showing why modern transistors like the Toshibas are better
than his old favorites (MJ802/4502, which themselves are
much better than 2N3055/2955 or TIP41/42).
Seek and you will find.
I used the TIPs in a project some years ago and I must say it outperformed many commercial SS amps.
Anyway there are better transistors nowadays, but as a rule of thumb the components should be "equilibrated" with the project you are using them in.
IMHO is only a waste to use super-special-high-bandwidth transistor in a "normal"project, on the other side is foolish to use "normal" components in a high-end design (of course if they are the weakest part).
Cheers
Andrea
Anyway there are better transistors nowadays, but as a rule of thumb the components should be "equilibrated" with the project you are using them in.
IMHO is only a waste to use super-special-high-bandwidth transistor in a "normal"project, on the other side is foolish to use "normal" components in a high-end design (of course if they are the weakest part).
Cheers
Andrea
Hi all,
No offence here..... Unless someone gave you a huge bag of TIP's and you want to use them, go with the Japanese transistors. They are right! They are better quality and performing than TIP's and a lot of 2N's....... This is from a tech who fixes amps and sees what manufacturers use. You know that manufacturers use the cheapest things they can find but they still don't use those old transistors. They need consistancy and good enough performance to last through the warrenty + try to give themselves somewhat of a good name..... My point..... Manufacturers are cheap. Although they could get the TIP's really cheap, they don't, as they won't perform good enough and consistantly enough to get out the door.
Just my 2 cents worth.....
With respect,
Chris
No offence here..... Unless someone gave you a huge bag of TIP's and you want to use them, go with the Japanese transistors. They are right! They are better quality and performing than TIP's and a lot of 2N's....... This is from a tech who fixes amps and sees what manufacturers use. You know that manufacturers use the cheapest things they can find but they still don't use those old transistors. They need consistancy and good enough performance to last through the warrenty + try to give themselves somewhat of a good name..... My point..... Manufacturers are cheap. Although they could get the TIP's really cheap, they don't, as they won't perform good enough and consistantly enough to get out the door.
Just my 2 cents worth.....
With respect,
Chris
I actually did run into a bunch of TIPs, that's why I asked. Also, my cousin burned a Phase Linear car amplifier because he tried to power light bulbs with it (don't blame me, it wasn't my idea), and I found a pair of TIP41s and TIP42s inside on the putput stage. Before he tried using the amp as a disco flasher, it sounded very good as a full range amp.
Hey Solid Snake,
I figured that's why you were inquiring...... I have an old Lanzar car amp that supposedly does 540W RMS into 4 Ohms per channel! The heatsink is about 22 inches long and weighs about 9 pounds... I worked at a repair shop and it was considered junk so I took on the task and took it home. I replaced all 12 IRFZ44 mosfets in the power supply and about 4 power transistors (TIP devices) There are 12 in each leg!!! 😱 Crikey-man!!!!!!! Now, in defense of your post, that particular amp was supposed to be the creme-de-la-creme at the time (early 90's) vintage, so......... I say, If you have em, use em, and see. They'll probably work fine! Matching will be key though as they usually aren't consistant at all.
Good luck and let us know what happens.
PS... If you know of a good project amp between 600-800 Watts, I'd like to know. My rails will be around 85- 95Volts.
Chris
I figured that's why you were inquiring...... I have an old Lanzar car amp that supposedly does 540W RMS into 4 Ohms per channel! The heatsink is about 22 inches long and weighs about 9 pounds... I worked at a repair shop and it was considered junk so I took on the task and took it home. I replaced all 12 IRFZ44 mosfets in the power supply and about 4 power transistors (TIP devices) There are 12 in each leg!!! 😱 Crikey-man!!!!!!! Now, in defense of your post, that particular amp was supposed to be the creme-de-la-creme at the time (early 90's) vintage, so......... I say, If you have em, use em, and see. They'll probably work fine! Matching will be key though as they usually aren't consistant at all.
Good luck and let us know what happens.
PS... If you know of a good project amp between 600-800 Watts, I'd like to know. My rails will be around 85- 95Volts.
Chris
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