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Old 27th February 2003, 12:48 AM   #1
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Default 2N3055 vs TIP41

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?
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Old 27th February 2003, 01:08 AM   #2
BrianL is offline BrianL  United States
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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.
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Old 27th February 2003, 02:25 AM   #3
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Why aren't the TIP's "decent" for power amps? What exactly makes a transistor good or bad besides power handling?
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Old 27th February 2003, 02:35 AM   #4
Duo is offline Duo  Canada
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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.
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Old 27th February 2003, 02:45 AM   #5
BrianL is offline BrianL  United States
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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.
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Old 27th February 2003, 04:05 AM   #6
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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?
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Old 27th February 2003, 04:40 AM   #7
sam9 is offline sam9  United States
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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.
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Old 27th February 2003, 04:48 AM   #8
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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.
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Old 28th February 2003, 01:51 AM   #9
sam9 is offline sam9  United States
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"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.
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Old 28th February 2003, 04:05 AM   #10
BrianL is offline BrianL  United States
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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.
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