So frustrating! I had a reply nearly as long as your post above, but accidentally hit some button and the entire thing evaporated. Oh well, maybe I will be less wordy and more to the point this time.
Thanks for such a thorough set of suggestions and explanations! This sort of advice is so valuable to me. I understood the part about the rectifiers right away. The part about the linear voltage regulators will take some research on my part to get up to speed on that. I think I almost understand the part about NPN emitter followers, though. I'll be using all of that as well as everyone else's advice as I figure this thing out. Glad the advice has not been conflicting! Gives me confidence that I'm headed in the right direction.
So, tacking a question on to this reply that's meant for anyone following the thread, since you've spent so much time already:
How do I know what generic components are best to replace the original parts? For instance, the tantalum caps come up a lot, but I assume when folks replace them, they don't use the same as the originals. What DO they use? There are so many types of capacitor, even in this one scope, and it's more than 37 years old. The large power supply caps are replaced with newer, smaller electrolytics, but I've heard that some brands are more reliable and last longer than others. What are some good choices?
I looked up one of the original rectifiers, an MDA960-3. I found a NOS of it on Ebay for almost $9 plus shipping. At that rate, this is going to get expensive very quickly. So what can I use instead? I assume that by looking up the specs on each original component that I end up replacing and finding something that meets or exceeds those specs, I'll probably be okay, but I could really use the voice of experience here.
I'm aware of Digikey and Mouser. I ordered some diodes from Digikey several years ago to build a rectifier that I used to convert the power from a hub generator on my touring bike to charge my phone as I rode. It even worked, although my buddy said the one I built for him killed his phone. Mine had some issues that I never resolved. I'm hoping to soon have the ability to design my own circuit, rather than copying someone else's, and have it be rock-solid! But, I digress...
Thanks again, Harvey!