Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements

[dlucy]

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing.

While following along with others' threads and trying to help out with "consider replacing these known-noisy transistors", I've tried to find a "top ten list" or "worst transistors" thread, but found none.

If there is a long-standing "which transistors go bad or go noisy and you should replace when you can" thread, please post a link.

If not, please contribute your "worst, replace ASAP" transistors and what you've replaced them with (understanding many transistors applications are different and the replacement won't always be right).

Warning: these are broad recommendations that WILL NOT BE CORRECT for all applications. It's up to you to do further research, testing. This is only a starting point guide. More detailed guidance is available in dlucy’s guide - how to find replacement transistors and in search results here on AK that you can do on your own.

Note: there are many variations of gain, HFE in the replacements listed below, compared to the original part and its application in your circuit. You should be careful in comparing the actual gain, HFE values you buy to the original part, spec... and potentially buy many more replacements than physically needed so you can test each and select the replacements that match, come closest to matching what your circuit application needs.

Note: some replacements below do not fully match the original component's specs (for example specification Ic of KSC1845 is less than specification Ic of 2SC458... but often the application circuit [in audio signal path] rarely exceeds the spec of the KSC1845, so it is often fine). It is up to you to test, measure.

Note: some replacements require the rotation of the device to accommodate a replacement ECB pinout device to work in place of a BCE pinout device.

Note: The new additions of the Central Semi 2n37xx-2n40xx devices is new to this list and has not been confirmed. More detail in this post.

Type              Replacement(s)                                     Failure notes
----------------- -------------------------------------------------- ------------------------------
2SA706 EBC TO202  KSA1220, 2SA1837, TTA004B*, MJE15033*              Gain deteriorates with age
2SA720 ECB TO92   KSA1013
2SA725 BCE TO92   KSA992, BC327*                                     Shot noise
2SA726 BCE TO92   KSA992, BC327*                                     Shot noise
2SA798            (2x) BC560B, (2x) KSA992 (note #1)
2SA809            KSA1381                                            Poor heat dissipation

2SC458 ECB TO92   2SC2240, KSC1845, 2N3707, 2N3708, 2N3710, 2N3711   Leakage, noise, static
2SC631 ECB TO92   KSC1845, 2N3707, 2N3708, 2N3710, 2N3711            Prone to failure, noise
2SC632 ECB TO92   KSC1845, 2N3707, 2N3708, 2N3710, 2N3711            Prone to failure, noise
2SC871 ECB TO92   KSC1845, BC549*, BC550*                            Leakage, noise, static
2SC1000           KSC1815Y                                           Leakage, noise, static
2SC1124 EBC TO202 KSC2690, 2SC4793, TTC004B*, MJE15032*              Gain deteriorates with age
2SC1312 ECB TO92  2SC2240, KSC1845, BC337*
2SC1313 ECB TO92  2SC2240, KSC1845, BC337*
2SC1318           KSC2383, KSC2690A                                  Thermal stress, thermal flex
2SC1344 ECB TO92  2SC2240, KSC1845, 2N3707, 2N3708, 2N3710, 2N3711   Static burst
2SC1345 ECB TO92  KSC1845, 2N3707, 2N3708, 2N3710, 2N3711            Poor mfg quality
2SC1400 ECB TO92  KSC1845, 2N3707, 2N3708, 2N3710, 2N3711            Static burst
2SC1451           KSC3503                                            Static burst, open circuit faults

* = wrong pinout order, so device will work but you'll have to twist and insulate the leads as
you move them to fit the original pinout order.

Note #1: A good thread on 2SA798 replacement using either KSA992F or ZTX795 can be found here: https://www.audiokarma.org/forums/i...nsistor-2sa798-is-there-a-replacement.281614/

 

[dlucy]

A couple threads on this with a few replacements:

http://www.audiokarma.org/forums/index.php?threads/noisy-small-transistors-in-g-3000.499623/

http://www.audiokarma.org/forums/index.php?threads/are-the-2sc1344-noisy-transistors.428489/

 

[drumbum]

I replaced some a949's and some c2229's in an onkyo that were very crackely. I have been told that pioneer used 'em often.

 

[Watthour]

How about a "Top 11" list instead. After all, this IS AudioKarma, and going to eleven is just the way it's done.

 

[elnaldo]

Already posted this in other threads, the 2sa798 double transistors always fail. I replace them without thinking 2 times. I use 2 low noise transistors like the 2sa992 or bc550 or 560 (I never remember wich # is the NPN and PNP )

 

[SoundOfSound]

 

[audiojones]

#1 offender on my list is Hitachi 2SC458 (if you've ever worked on an AKAI tape deck amplifier board you know what I mean). They're used in all sorts of gear from most manufacturers and they are major troublemakers.

 

[gslikker]

What would be interesting, which are the same era types of npn transistors used as much as the 2sc458 in the same type of spots which "never give trouble" ?

 

[audiojones]

What would be interesting, which are the same era types of npn transistors used as much as the 2sc458 in the same type of spots which "never give trouble" ?

2SC945 is one that rarely seems to cause trouble. I think a lot of the 458s were pushed too close to their design parameters in many circuit designs which didn't help things.

 

[larryderouin]

2sa763 used in a lot of PIONEER stuff is usually bullet-proof, compared to the 2sa725 or 2sa726 it replaces.

 

[Fredrik 1977]

they say the most stupid questions are those never beeing asked.

say i´m repairing some amp without the schematics it happens sometimes right! i come across a shorted transistor with the text C1381. is there a way to tell if its a 2sc1381 or ksc1381?

 

[audiojones]

they say the most stupid questions are those never beeing asked.

say i´m repairing some amp without the schematics it happens sometimes right! i come across a shorted transistor with the text C1381. is there a way to tell if its a 2sc1381 or ksc1381?

Same basic thing, KSC1381 is a modern equivalent for 2sc1381

 

[Blue Shadow]

I asked in DIY for transistors that are routinely replaced for whatever reason.

http://www.audiokarma.org/forums/in...-of-transistor-that-should-be-changed.514528/

In that thread this list of substitutions, not necessarily ones that gotta go, was supplied along with a number of individual suggestions.

http://hudsonvalleyhifi.com/technical-data/transistor-substitutions

Now we just need all the information to show up in one nice chart like @Watthour has put together.

 

[Fredrik 1977]

how about bc557 and 558 as replacement for 2sa726 and 725?
i prefer to use bc, bd and so on. they are easier,cheeper to order here.

its recomended to replace all 725/726 i ever come across?

 

[Oldsansui441]

bc327 for 2sa725/726 and bc337 for 2sc1312/1313.
Yes it is recommended as you say, along with their counterparts as above.

 

[ZOOM]

how about bc557 and 558 as replacement for 2sa726 and 725?
i prefer to use bc, bd and so on. they are easier,cheeper to order here.

its recomended to replace all 725/726 i ever come across?

Never use bc/bd type transistors in place of Japanese types (2s), they are never equivalent and always a major downgrade in performance, provided it will even work in the first place.

 

[Fredrik 1977]

Never use bc/bd type transistors in place of Japanese types (2s), they are never equivalent and always a major downgrade in performance, provided it will even work in the first place.

well the equivalent part of that statement i can buy....not really shure what u mean

 

[dlucy]

I have edited the original post above and added a table with those transistors in the posts (so far) and their suggested replacement transistors. Please take a look and point out what I've missed or typos.

 

[gslikker]

I replaced some a949's and some c2229's in an onkyo that were very crackely. I have been told that pioneer used 'em often.

The little bit newer transistors might be the next "worst transistors".

Anyway an interesting thing is the toshiba datasheet of these suggest lesser reliability when continuously operating near the limits, even if this is within spec. Although this probably applies to all semiconductors, one does not always see this mentioned.

 

[Fredrik 1977]

I have edited the original post above and added a table with those transistors in the posts (so far) and their suggested replacement transistors. Please take a look and point out what I've missed or typos.

thank you! i understand u guys in the us dont care to much about bc´s..but its much less hassle for me to use them.