Fundamental difference between BC559C and BC557B

[Dave Turner]

I've just come across the specs for the 'Curious C-beeper'.  The version I've seen specifies BC559C and BC549C transistors.
The closest I have in stock are BC557B & BC547B respectively. At first glance they seem to have similar specs.

Clearly I'm missing something fundamental and important. Would someone point out what I'm missing please?

[madires]

Check out the datasheet V_CEO is 30V for BC549 and 45V for the BC547. That should be fine. But hFE could be an issue since C means 420-800 and B means 200-450. Try to find BC547Bs with an hFE of about 400. The same applies to the BC557B.

[Dave Turner]

Madires - Thanks it's so easy to miss the obvious. If I may, however ask subsequent question; suppose I had BC557Cs with hFE 420 - 800 what is the difference between them and the 559C?

I'm going to experiment anyway. but whilst I usually understand the overall picture I'd like to properly comprehend the subtler issues.

[David_AVD]

BC5x7 and BC5x9 have different Vce specs.

[Dave Turner]

David_AVD - thanks. I finally found the Fairchild data sheets which compare the BC556/7/8/9 & 60. It's a little easier to spot that V_CEO and V_CBO varies.

[Tube_Dude]

BC559 and BC549 are lower noise versions of the BC557 and BC547 respectively.

They are usually used at input stages and where lower noise is determinant.

There are  some voltage ratings differences, as you can see in the data sheet, and the suffix letter (A,B,C) show the hFE variation interval...

[Dave Turner]

Tube_Dude - cheers. I was wondering whether the 557 would be a suitable substitute for a 559 in a curious c beeper, because that's all I have to hand. I guess the only answer is to breadboard it and check it.