Re: Transistor equivalent to UK's BC183B?
- From: Mark Aitchison <MarkA@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 10 Feb 2007 21:51:14 +1300
hmz6@xxxxxxxxx wrote:
Hi all,
I am trying to rake together the components to build a metal detector.
The plans are from the UK, and I'm US. The plans call for BC183B
transistors, and I was wondering if there was an easier-to-get
equivalent.
The BC183 is a plain vanilla NPN silicon small-signal transistor (a bit out of date, although I think I have one), and the "B" gain group is the middle of the range gain (hFE 240-500 at 2mA Ic and Vce=5; typically 330). Not especially high voltage, not especially low noise. So quite a few transistors should fit in there. Unfortunately, unless you have the -A, -B and -C (or -16, -25 and -40) gain range specification, which many Pro-Electron (BC... - most European small signal transistors) you may have to go through transistors like PN100 or 2N3569 with a gain tester, as others have suggested. The best idea is to hunt down something like the BC549B (see below).
For what it's worth, the background to that family of transistors goes something like this: the "BC" at the start identifies a silicon audio transistor (using the Pro-electron naming scheme, which I think is more helpful than JEDEC), and is reasonably easy to find explained on the internet, but there isn't exactly a formal system to the number part... what is NPN or PNP, for instance. But back around 1966 a family of TO-18 silicon transistors came out, BC107 to BC109, that not only became very popular, their number system became popular and so was copied by many other transistors, up to the present day. This is how it works: ...7 means high voltage, ..9 means high/gain and low noise, and ..8 means cheap - not especially great in any way. This was followed by BC177 to BC179 for PNP counterparts. Then BC147-9 and BC157-9 for "lockfit" plastic casing versions, and various other plastic case versions with the middle digit EVEN for NPN and ODD for PNP. A lot (but beware: not all) BC... transistors use the ..7/8/9 tradition, a common pinout that goes e-b-c (dating back to the AC126 and OC71), and odd/even middle digits indicating PNP/NPN... exceptions being ones like BC338, BC640, etc. Standardisation is a wonderful thing in the electronics industry; it is just a pity there are so many different standards to choose from!
An even more well-used tradition/standard is the gain group letters at the end: A for low gain, B for middle gain, and C for high gain. While the BC..7/8/9 family was becoming popular, Texas Instruments had Pro-Electron transistors BC182/3/4 (NPN) and BC212/3/4 (PNP) with high voltage/cheap/high gain signified by the last digit a bit like the 7/8/9 family. But they had letters like "L" at the end giving the pinout (e.g. b-c-e), not the gain. Quite a few US manufacturers (including Motorola) made transistors with Pro-Electron names, many making the BC182/3/4 series. It is interesting to see them swing, over time, to follow the -A/B/C suffix giving gain ranges (which is nice), while some European brands eventually moved away from that to use -25, -40 etc to show 250+ gain, 400+ gain, etc!
Back to the problem at hand: Many transistors popular in the US (e.g. the 2N4124, and 2N930 - is that still popular?) *may* have the appropriate gain, but they often lack the restricted gain range marking that ensures a particular transistor will have enough gain. You may have to try a few on an hFE tester to get one that is suitable. Or you could try something like a 2N5088 and know you have enough gain, but it has less current capability and base-emitter reverse voltage rating - which might not matter in your circuit, but I cannot be sure. Some of the good 2N.... equivalents, that are pretty likely to have a high enough minimum gain, are somewhat rare (e.g. TO18 can). There is, however, a really good answer...
The best idea, as Eeyore suggested, is to get one of those many transistors like BC547B, BC549B, etc that have the gain range specified; these are pretty common at mail-order parts suppliers like futurelec, jaycar and digikey, and pretty much the transistor-of-choice for general circuits from Australia to England so not likely to go obsolete any time soon. But not everyone stocks the restricted gain range versions, or specifies them in the catalogue (e.g. Jaycar simply says "BC549" but you are likely to get BC549B). Shop around for a supplier that advertises a BC549B or whatever - they are plentiful.
Other examples: BC109B, BC168B,BC169B,BC547B,BC548B,BC549B,BC546B, or BC550B. The -C gain group is even better. If you have to get a BC54- transistor without the gain group specified choose the BC..9 or BC550, since they pretty much always don't include much below a gain of 250.
Mark A
.
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