russian PDP-11 like K1801BM2 CPU Startup reading w/o address?

I feele this is actually a poor deisgn, in that the gain from the op-amp (and thus the exact value of the resistor you are tweking) that you need depends on Wein bridge network components how well balanaced they are, for example). It may work on the breadboard while you're watching it, but it could drift one way or the other with temperature changes, etc. It's not somethign I'd do in anything I wxpected to keep on working. The normal trick is a light bulb (or a suitable vacuum-encased thermistor) to act as a non-linear element. IIRC mo purely linear system can produce stable oscillations (any small change will either cause said oscilaltiosn to colalpse to zero or to grow ithout limit (or more practically untyil the signal hits the supply rails). I am sure we all know the stroy of Fred Terman and a certain research student. It is and it isn't. You certainly knew what uou were doing annd why (settign the gai nof the amplifier correctly yto just compensate for the loss in the RC network), but for the reasons given aboove, I don't think this a good design practice. For simialr reasons I am wary about the uses of resistor and capacitor substitution boxes 9essentially boxes with all the prefered values of R's or C's in them with switches to seleect them). The have 'proper' uses (e.g. to see how a circuit's behaviour is canged when a componnet is varied, they have an 'improper' use ('Lets fiddle with this component and see if we can get it to work). But then all tools can be misused. -tony