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How About These Transistors ?
How About These Transistors ?
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Old 14th February 2018, 12:44 PM   #1
Wavewhipper is offline Wavewhipper  United States
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Default How About These Transistors ?

I have been troubleshooting for a long time and recently took to studying the finer details of transistor design and refinement. Many output driver transistors look as if they were intended for beta independent circuits, the beta curves are pretty bad looking humpty dumpties.
How about these ? They are sort of rare, low volume things, I figure showing them may boost sales well enough to prolong the product life. I hope they keep making them. I bought 15 pairs for evaluation.
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File Type: pdf KSA1220A.pdf (195.5 KB, 39 views)
File Type: pdf KSC2690A.pdf (170.1 KB, 8 views)

Last edited by Wavewhipper; 14th February 2018 at 12:49 PM.
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Old 14th February 2018, 12:49 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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In feedback amps the beta curve is pretty much irrelevant.
I have used switching mosfets and IGBT's with no problems in audio amplifiers.
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Old 14th February 2018, 01:06 PM   #3
Mark Johnson is offline Mark Johnson  United States
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How About These Transistors ?
I use those in the final output stage of a headphone amp, and they work just fine. However the SOA is so tiny that you'd need BUDZILLIONS of them in parallel to drive a typical 8 ohm loudspeaker box.
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Old 14th February 2018, 02:39 PM   #4
Wavewhipper is offline Wavewhipper  United States
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I have them in mind for an Szikali driver pair for these. Aim is 200watt with an option for doubling the output transistors. I do get nit-picky but figure the easier I can get them linear without need for correction, the end result may be better yet. Since I am not making a million of them I can ignore $3.50 output transistors instead of $1.50 - $2.50.
It is a try to replace a 30 year old mosfet design with four hard to get $15 each lateral mosfets.
Above all, a learning experience.
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Last edited by Wavewhipper; 14th February 2018 at 02:47 PM.
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Old 14th February 2018, 08:11 PM   #5
wg_ski is offline wg_ski  United States
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They are a little small for drivers in a 200 watt application. 100 watt is more appropriate.

These may be on the way out - a lot of similar devices like the A1507/c3902 pair have already bit the dust. Similar devices in SMD packages will likely still be available for years, but if you want isolated TO 126's that are NOT the BD139 type you probably ought to stock up while you can. It is only a matter of time before they all disappear.

Flatness of the hfe curve is far more important on the driver transistor than it is on the output. Nice to have in both places, but more critical on the driver.
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Old 14th February 2018, 08:21 PM   #6
gholl is offline gholl  United Kingdom
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Quote:
Originally Posted by Mark Johnson View Post
I use those in the final output stage of a headphone amp, and they work just fine. However the SOA is so tiny that you'd need BUDZILLIONS of them in parallel to drive a typical 8 ohm loudspeaker box.
I worked for a company called ILP Electronics many years ago and joined them at a time when they were using output transistors designed for an 8 ohm resistive load. When I showed the MD/CEO the load curves relating to a real loudspeaker (+/- 60 degrees phase shift) and saying that the design needed three pairs of devices in parallel, I hit a brick wall. Luckily, I'm now free to design what I like, how I like.
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Old 14th February 2018, 08:29 PM   #7
wg_ski is offline wg_ski  United States
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Those things liked to blow up more than Phase Linears did. Even STK modules tended to tolerate being played loudly better than the ILP's. Back in those days when they didn't fake STK's anyway.
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Old 14th February 2018, 08:44 PM   #8
gholl is offline gholl  United Kingdom
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I worked for ILP longer than I should have done. I feel ashamed and sorry. I then went on to design in a manner that I was comfortable with. Lucky me.
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Old 15th February 2018, 01:05 AM   #9
Refugee1 is offline Refugee1  United Kingdom
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Look at BF469/BF470.
They should be easy to get hold of and are a slightly higher voltage rating.
Otherwise they are pretty much the same.
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Old 15th February 2018, 02:31 AM   #10
indianajo is offline indianajo  United States
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Originally Posted by Refugee1 View Post
Look at BF469/BF470.
They should be easy to get hold of and are a slightly higher voltage rating.
Otherwise they are pretty much the same.
Not in the US. Digikey no reference, newark references the NTE39 with all the specs left off the datasheet.
digikey has actual stock of ksa1220ay and ksc2690ay in Minnesota. Farnell has theirs in the UK only.
20 watt 155 mhz drivers, 200 ma soa at 70 v. cool. I just bought four 2n5682 in the TO39 metal can for drivers at $1.88 each. These are ECB instead of EBC and the heat sink would be cheaper since it has a flat surface. I may buy some, they would be cheaper than TO39 heat sinks.
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