KSC945 looking for 2Nxxxx equivalent

[soggybag]

I’m working on a synth project that calls for a single KSC945. This is an NPN BJT. I have a box full 2N…. and BC… Parts one of these has to work. What would be a good replacement?

Type Designator: KSC945

Material of Transistor: Si

Polarity: NPN

Maximum Collector Power Dissipation (Pc): 0.25 W

Maximum Collector-Base Voltage |Vcb|: 60 V

Maximum Collector-Emitter Voltage |Vce|: 50 V

Maximum Emitter-Base Voltage |Veb|: 5 V

Maximum Collector Current |Ic max|: 0.15 A

Max. Operating Junction Temperature (Tj): 150 °C

Transition Frequency (ft): 300 MHz

Collector Capacitance (Cc): 3.5 pF

Forward Current Transfer Ratio (hFE), MIN: 40

[MikeA]

alltransistors.com has an equivalency search tool
https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=0.25&ucb=60&uce=50&ueb=5&ic=0.15&tj=150&ft=300&cc=3.5&hfe=40&caps=TO92

[mozz]

Wouldn't that be the same as a 2SC945? They are not that hard to find. Also, is there a letter after the numbers, such as A,B,C, that would be the gain range instead of a plain old 945, which would have more of a spread.

[Mark Hammer]

Keen's rule: when in doubt, use a 2N5088.  But a garden variety 2N3904 will do just fine.

[pacealot]

And, of course, mind the pinout, since many (but by no means all) of the 2SC/KSC series BJTs come in BCE rather than CBE (or, depending on your orientation, ECB rather than EBC)...

(I enjoy a good 2N3707 or 2N3708 as a pinout-correct sub in these situations, but their specs aren't much closer to the 5088/9 as Antonis points out below...)

[antonis]

2N5088/89 are far away both from C-B / C-E max voltage (35/30 & 30/25) and ft (50MHz)..

[Rob Strand]

Fairchild produced KSCnnn transistors which were *functionally* the same as 2SCnnn transistors.
The difference (IIRC) comes about in that KSC's have the common US transistor pinouts whereas the 2SC follow the common Japanese transistor pinouts.

As Mozz already mentioned 2SC945 are *very* common.

I reckon a 2N3904 would do it.
I checked the fairchild datasheet.   The KSC945 does have a suffix letter indicate the gain category.  For example,

Y      hFE = 120 to 240          =>  2N3904
GR   hFE = 200 to 400          =>  BC547B

[ElectricDruid]

Keen's rule: when in doubt, use a 2N5088.  But a garden variety 2N3904 will do just fine.

Yeah, that would be my approach too - in general, stick either 2N3904 or 2N3906 in depending on whether the transistor to replace is NPN or PNP, and only after seeing if that works would I worry about whether I need anything else. I've always been surprised by what I can get away with!

[PRR]

A circuit is hardly ever designed for a specific transistor. (Jensen 990 _is_ specific to the LM394; several computer gate cards were specific to some part with good price and availability; mostly transistors are jellybeans.)

I was taught "assume hFE>50". This very often works, if the designer was competent and serious. (There is a second layer of uses where hFE>300 is better performance or even necessary.)

I have never seen 60V inside a synth. 30V ought to be ample.

[Rob Strand]

There's plenty of examples where the correct gain helps the cause.    Boss and Roland are very deliberate in the choosing the best parts for the job - it's pretty clear their engineers know what they are doing.

If you understand the design you can have some confidence about subbing parts where it doesn't matter.

[soggybag]

Thanks for all the replies. I’m going to give it a try with a good old 2n3904. Which looks like it has a flipped pin arrangement.