If you could only buy 10 (BJT)transistors, which ones? - diyAudio
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Old 27th September 2011, 04:40 PM   #1
cbdb is offline cbdb  Canada
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Default If you could only buy 10 (BJT)transistors, which ones?

I want to start playing with audio circuits (power amps mostly) so I need some "generic" transistors. I will need small signal, drivers and power (NPN and PNP). I want to start with BJTs. I know there are thousands of transistors out there but I only need a couple of version of each type. So I guess maybe 10 or 12 specific transistors. Should be easy right? So I thought. I decided to go with BCE560 as one of the transistors. Went to the Mouser site and searched for BCE560 and 18 different transistors came up from 3 different manufacturers with prices varying from 10 to 60 cents per unit. For me to look thru all the data sheets and compare them would take me an hour. That times 12 transistors seems like a lot of time and I would still be guessing. So I decided to use this wonderful resource and ask the ones with experience.

Heres what I need. Good for audio, not real high voltage, not expensive, decent noise (for the small signal at least), available, (lead solder?) and the exact model number and manufacturer. Thanks in advance.
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Old 27th September 2011, 05:08 PM   #2
Mooly is offline Mooly  United Kingdom
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Common easy to get types if you are just starting out. Nothing exotic, nothing expensive... things that will work

Noise isn't an issue... that depends more on the circuit itself unless you are working with microphones/tapeheads/rf amplifier front ends etc.

2N5551 npn small signal
2N5401 pnp small signal complement to above
MJE340 npn high voltage suitable for driver
MJE350 pnp complement to above
MJ21194 npn high power TO3 packages output
MJ21193 pnp high power TO3 packaged output complement to above
[these are available as flat pack packages as type MJL21194G and MJL21193G if prefered].

BC546 npn small signal
BC556 pnp small signal

That's 8 to be going on with and would let you build most designs on these forums.

TIP41C and TIP42C general purpose npn and pnp power types are useful for regulators etc.

The letters on the end of a device eg BC556C usually imply a gain group and C is the highest. That said any circuit should be designed not to be super critical.
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Old 27th September 2011, 10:24 PM   #3
cbdb is offline cbdb  Canada
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Thank you Mooly, does manufacturer matter or should I just get whats cheapest/easiest to find.
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Old 27th September 2011, 11:43 PM   #4
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2STC5200 + 2STA1943, less than $1US at Digikey
2STAxx and 2STCxx Transistor Series - STMicroelectronics | DigiKey

Wherever you live, buy the locally made brand.
Anything touched by an importer might be fake.
Especially famous brands, however great the
real thing might actually have been...

Nothing wrong with Mooly's MJ2119x except price, $5 ea

Last edited by kenpeter; 28th September 2011 at 12:10 AM.
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Old 28th September 2011, 12:20 AM   #5
cbdb is offline cbdb  Canada
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Thanks kenpeter, since knew to this I expect to burn a few transistors up, so cheap alternatives that are close are great. As far as local transistors, I dont know if there are any here in Vancouver. What about using Digikey or Mouser?
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Old 28th September 2011, 12:33 AM   #6
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Hey, 2STC5242 and 2STA1962 only 65 cents...

Digikey and Mouser are reputable distributors, not manufacturers...
They won't sell you a known fake, but they do sometimes get fooled.
I don't know who manufactures in Canada, probably same as US.
You can only order from a distributor anyway...

I was only saying, if I lived in Tokyo, I'd buy Toshiba, Hitachi, or Sony.
If I lived in Texas, I'd buy ST... Fewer greedy hands in between.

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Last edited by kenpeter; 28th September 2011 at 12:44 AM.
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Old 28th September 2011, 12:36 AM   #7
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MPSA42. Small signal for LTP, current miror and constant current source.
MJE340/350 VAS.
IRFP240/9240 high power mosfets.
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Old 28th September 2011, 12:46 AM   #8
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It depends on what's available to you really, there are some transistors that will improve on Mooly's suggestions (as far as I am aware) and they wont cost any different, but they aren't critical I guess unless you're really trying to fine tune or push performance to the limits.

Something like the 2STC5949/2STA2121 would make for a good alternative to the power devices. These tend to be what are expensive so perhaps would be the one device you might want to get picky about if you want to save a few pennies.

Different low noise small signal transistors will give you a small benefit, but as Mooly points out this is circuit dependent. A higher beta/hFE on the input pair should help with matching and create less offset but this can also be circuit dependent and also controlled via additional circuitry.

Often when you get 10 transistors of the same type from the same manufacturer it will be because of the hFE classification. I don't think I've encountered a situation (I'm not that experienced with this stuff I must say) where a lower hFE is actually better, but they sort the transistors into batches of different hFE, if you can buy ones with higher hFE, without paying that much more, then I think it'd be recommended for you to do so. Something like the KSC1845 and its compliment the KSA992 would make for good small signal transistors and they cost peanuts.
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Old 28th September 2011, 01:03 AM   #9
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2STC5949 NPN is definitely priced right at 95cents,
2STA2121 PNP compliment at four times the price! that gets you...
Beware, many of the complimentary pairs are priced asymmetrically.
NPN are slightly higher SOA, and so may be priced for broader use.
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Old 28th September 2011, 06:19 AM   #10
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by cbdb View Post
Thank you Mooly, does manufacturer matter or should I just get whats cheapest/easiest to find.
As others have said you must buy from a reputable source.
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