I am working my way through Make: Electronics. For some experiments in this book, you need a 2N6027 programmable unijunction transistor (PUT). The shop I am buying my parts from doesn't have this exact model, but the 2N6028. The combined datasheet for both models shows some differences. I am wondering whether they are similar enough for simple experiments are whether I should try finding another one that matches the 2N6027.
They share the same datasheet, and I think the differences almost certainly won't affect the experiment (oscillator?)
The only significant difference I can see is the peak current on the 2N6028 is lower, which means it will turn on a bit sooner. If set up as an oscillator I think this will just produce a lower amplitude waveform.
Disclaimer - I have only used one of these once a long time ago (almost unheard of nowadays) so I wouldn't put this in writing (er, hang on...)
A good tool is www.findchips.com. Both mouser and digikey stock the 2N6027, and it is cheap for such an old beast. www.reichelt.de is even cheaper. If you don't want to go out of the country: I sell the 2n2646: http://www.voti.nl/winkel/p/T-2N2646.html .
Digikey has both in stock.
I see you are in the Netherlands - I don't know how accessible Digikey is there.
Datasheet for both is here from ONSemi.
As Oli notes, the peak currents are different.
The 2N6028 peak current is about 10% of that for the 2N6027.
This would make major differences in resistance or capacitance or time values in a given circuit. Definitely usable but you may learn a bit more than expected along the way :-).
Other parameters vary between the two parts but are probably close enough so as not to make a major difference.
UJTs are interesting devices and well worth knowing about, and you can do some fun things with them that are not easily done with other single devices - but they are relatively little used in modern circuits.
You have many "easy to find in stores" replacements / equivalents for the 2N6027 PUT (Programmable Unijunction Transistor).
The following are the replacement parts listed in www.icreplacements.com:
2N6116 2N6119 MPU131 MPU231 SK3628
Hope it helps you to finish your project. :)
Complete information source:
I've encountered a similar problem, but the local shop doesn't carry the 2N6028 either. They do carry the the NTE 6402 (TO-92/TO-98), however.
Looking at the data sheet, compared to that for the 2N6027, I think that the NTE 6402 could serve as an equivalent replacement component. I'd be happy to let anyone check my work on that, though.
The dutch ( in Groningen) store okaphone sells the 2N6027 http://www.okaphone.nl/ for 95 euro cents piece. they also have a webstore order.