On Jan 15, 22:54, Tony Duell wrote: Transistor PC Towers is excellent, and I'd not be without my well-thumbed copy. I suppose I should buy a newer one some day. However, it seems like every time someone in Japan or other some other parts of the Far east designs a circuit, they design or specify a new transistor for it -- a transistor that is almost identical to some existing device, but has with some minor, often trivial, tweak. I suppose it may save some corporation a fraction of a yen on each of hundreds of thousands of units. Or perhaps the way it works is that a designer says "I need a transistor with the following parameters..." and someone makes a batch to order rather than using an existing design (for which they have no stock, because of just-in-time stocking) and the made-to-order gets a unique number, more like a batch number than a type number. That's why I bought the Japanese manuals (there's one for FETs and one for diodes as well as the transistor one), and more particularly, why I posted the main operating parameters. There are probably dozens of relatively common types that could be used as substitutes for a 2SB1243. If you need one, it's just a question of looking in your favourite sales catalogue and going down the list until you see something close enough. -- Pete Peter Turnbull Network Manager University of York