The BC10x series of transistors.

[Steve Anderson]

Passing time wandering though the past issues of the newsletters I noticed that the venerable BC107, BC108 and the BC109C turn up in a lot of schematics, even recent ones.

This series was launched in the 60s and so is now over 40 years old. These days there is no reason to use them, there are better and cheaper devices that are available.

The BC54x series were launched to be drop-in replacements and at the same time the specifications were enhanced. The BC548C was to replace the BC109C. The BC109C was generally used in low-level pre-amps so the noise figure was improved from 4bd to 2db i.e. the BC548C is quieter. Other parameters were improved but they don't really apply to NBTV or audio use. The Hfe (small-signal current gain) for BC548C is very slightly higher.

The subject of cost, I checked a number of UK retailers prices and on average the BC109C was 40p whereas the BC548C was 10p in small quantities. I also noticed that some don't carry the BC10x series at all anymore.

My suggestion is that once you've used up your stock of BC10x series devices, don't buy any more!

Buy 100 BC548C's, get a quantity discount and use them exclusively where any BC10x device is specified. There are differences between devices in the BC10x series, just like in the BC54x series, but in most designs used for NBTV it will make little or no difference.

One thing to watch though, the pin-out is different, one could easily get caught out if using a PCB with a component overlay.

Steve A.,

Edit. In fact the pin-out is the same, it's just in a straight line instead of a triangular arrangement - easier.

[AncientBrit]

Good point Steve but there are 2 reasons I use them.

I've got lots of 'em, and BC477's as well.

And the live can makes 'scope probing to the output (usually the can in common emitter stages) easy.

Regards,

Graham

[Steve Anderson]

Indeed, use up whatever you have right now, but (in some years agreed) you'll find the BC10x series harder to get and then there's that approximate 4:1 price ratio.

Not wanting to upset you guys, 100-off BC548Cs from my supplier here comes out to £1.50 including VAT. Maybe I should buy 1000 and send then on to guys, you can then divvy them up. !000 wouldn't even weigh 200 grammes and be a little cheaper, the first quantity price-break is at 250-off.

The point about probing the can is valid, but I've got so used to plastic-cased transistors I'd forgotten that bonus.

Steve A.

[Harry Dalek]

I am never 100% sure in trany replacements i do feel better you saying use the BC 548..its for me i don't want to waste my time desoldering a mistake transistors can be fussy little buggers at times.

I only have a few of the early can type tranys left i suppose they have one thing over the new plastic case ones remove the top of the can and you have a photo transistor i am told never tried it my self.

[Steve Anderson]

The reason semiconductors are sealed is to keep moisture in the air out. You can cut the top off a tranny and make a photo-transistor but wonder how long it would last? A bit like letting air into a tube/valve except the degradation would be instant!

What has made the metal can tranny fall out of favour is it's that hermetically sealed encapsulation, it's that that's the expensive part, otherwise what's inside is basically the same cost to produce.

Of course this cannot apply to power transistors and a compromise has been reached there for the same reason, long live the TO3. (The original 2N3055 case).

Steve A.

[dominicbeesley]

Thanks for this pointer Steve,

I have to admit to not being a component connoisseur, I tend instead have a few "standard" parts and make them work all over the shop. All my recent NBTV experiments I've used BC337/327s for any general purpose low current stuff and BF245s if I need a FET. Power transistors are whatever I can salvage from the junk pile or have lying around.

I'm the same with valves though they do tend to require the right valve id replacing but when homebrewing you can usually get by with a handfull of types. My current project is an NTSC colour decoder using valves. It uses two valve types: 6n16b-v double triode and 6j1b-v pentode. Why? Cos I got a load for cheap and they don't even need sockets.

How do you guys pick components? Do you go to your databooks and pick the most appropriate B/gain/etc or like me just check the power rating and hope...

[AncientBrit]

There is a down side to metal can transistors.

Internal tin whiskers can grow from can to chip and cause havoc.

Cheers,

Graham

[Steve Anderson]

I tend instead have a few "standard" parts and make them work all over the shop. How do you guys pick components? Do you go to your databooks and pick the most appropriate B/gain/etc or like me just check the power rating and hope...

I tend to keep my stocks to the minimum varieties possible too, especially discrete devices which I don't often use these days. Only if a special requirement that needs something out-of-the ordinary do I do some research. I tend to work backwards as it were. I check what's available here and dig out or download the data-sheets which I do study quite intently.

When you see a 2N2222 or a BC-something on my schematics I am actually using 2SC1815's, (Toshiba) they're equivalent and dirt cheap but I would think unknown outside Asia. The 2SA1015 is its compliment.

Steve A.

[M3DVQ]

last time I bought transistors I got a bag of 100 BC548s... There's a reason they're called "general purpose" - when you only have two bags of transistors it makes it *really* easy to decide what to use! ("do I need npn or pnp?")

[Steve Anderson]

Exactly my point. A bag (as you say) of 100 BC548s (NPN) and another 100 of BC558s (PNP). Aside from power devices, RF stuff and perhaps MOSFETs 95%+ of the time that's all you're likely to need.

Steve A.