Firstly - thanks very much to Vocky, Bundevski and all the other bright sparks for working to fix this problem and posting their diagrams, instructions and experiences on here.
I really want to build Bundevski's EGR cheater (Well done to you!). It makes sense to have a completely solid-state circuit - no contact bounce or moving parts to wear out, faster switching speeds, etc... I have just one question about this, that someone on the forum may be able to help with. The answer should be beneficial to anyone browsing in the future too. My question is: Can any other transistors be used in place of the BC640?
The reason I'm asking, is that I can't get hold of a BC640 transistor and there are very few sources that list equivalents. Those that do, tend to disagree as to /which ones/ are equivalent. As far as I can tell it's just a general low-power, low-frequency PNP transistor, but I'm just wondering if any LP/LF PNP transistor would do (for instance, a 2N5401, BC556B, BC557C...) - none of the ones I can find are an exact equivalent of the BC640. The BC640 seems to be able to cope with Vce=80v, Ic=1000mA, P=800mW, and Hfe (beta/gain/whatever you want to call it) is somewhere in the region of 40-250. As far as I can tell from the circuit diagram, the most Q1 would ever have to cope with would be 12v and a handful of mA. I'd guess that any such transistor I chose would be able to cope with this, I'm just worried in case Hfe is critical. If I selected a different transistor, would the different gain mess up the circuit and stop it working? My electronics knowledge is a bit rusty so I don't really trust my working-out on this one.
Thanks everyone for all the hard work, and thanks in advance to anyone who can answer this. A range of suitable transistor operating parameters, (or even a couple of suitable alternative transistor part-numbers) might be really helpful to anyone wanting to build this circuit.
