Mad Phil gave me his EMI Go-Kit, which contained a Tek P6401 logic probe (along with a short ton of ferrite cores):
It’s slightly younger than dirt (copyright 1974, please forgive me) and still works fine on TTL-level logic. The red & green indicators use tiny grain-of-wheat incandescent bulbs, of course, so the thing draws nigh onto a quarter of an amp with both lights on.
The front of the instruction card shows what the blinky lights mean and the back gives the specs; it’s doubled up so you can pass one along to a friend:
If you have one that doesn’t seem to work, check the internal thermal fuse: tack it back down with a hot dry soldering iron and it’ll probably outlive you…
The Smell of Molten Projects in the Morning 