[M452] > that the original appears to use a 2k 10-turn pot, and a 7440 output buffer, > neither of which are in my rather extensive junk box. > In fact the 7440 are rather rare, and I see the cheapest I can get them for > is around $4.00 each.
True. But you don't need either to build and test the oscillator circuit. The 7440 is an output buffer, if you want to build a test version of the entire module you could stick a '20 there or just about any other TTL inverting gate. But I was thinking of just testing the oscillator part which is Q1 and Q2 (again the other 2 transistors are buffers) The preset clearly sets the frequency. You could build the oscillator with say a 1k resistor there at least to put a 'scope on various points to understand how it works. > I am really used to RF circuits so am puzzled there is no inductor. It kind > of looks like a Darlington Pair but it isn't. RC oscillators have been around since the 1930s..... > > I will leave the flames about Spice and simulation packages in general for > > another day. > > You are touchy. Would it help if I used the original Spice2 written in > Fortran IV. It still works. Sadly I don't have a real mainframe but have to > use Hercules to run it.... OK, I sort-of forgot the smiley, but only sort-of. The problem is that people try to understand a circuit by throwing it on the simulator and really don't understand what is going on at all (this assumes the simulator gets it right which is not always the case). I prefer to think about it. work out how the capacitor (there is only one!) charges and discharges, since that must be the key to the oscillations. -tony
