rjr@mgweed.UUCP (Bob Roehrig) (11/12/85)
After rebuilding the power supplies for my Heath 105 scope, I also had quite a bit of vertical drift. The drift was caused by the power supplies that power the vertical amplifiers (among other things). I had used 78xx type regulators for the positive supply but used zener-to-pnp series pass for the negative supply. After finally obtaining the proper 79xx type negative regulator and replacing the zener referenced supply with that, the drift went away. The vertical amp has a lot of gain and ANY power supply variation will cause drift. I have found that while the absolute value on these 78xx and 79xx regulators is not super good, they are super stable and drift-free. In other words, if you want EXACTLY 5 volts, you may have to hand pick one from a dozen or so. Bob, K9EUI