The original 1N270's used in the Gottlieb switch matrix were used as a switching diodes instead of rectification. 1N270's were germanium diodes = expensive; very few germaniums made anymore. Advantage for these is they have a very low maximum forward voltage drop. You need a low forward voltage drop when used in a system such as Gottlieb's TTL level switch matrix.
1N4148 diodes are switching diodes and are intended for use in signal switching applications such as a switch matrix. The don't have as much parasitic capacitance, they have a fast response time, and they are rated at the same forward voltage drop as the 1N400x rectifiers on paper but in reality have a much lower forward voltage drop.
1N400x diodes are rectifiers that are intended for rectification of AC power into DC power. They don't have a fast response time, they have a lot of parasitic capacitance (in comparison), they have a high forward voltage drop. They're not intended for use in switching systems.
The most important feature is the forward voltage drop -- very important in a Gottlieb TTL level switch matrix, less important in switch matrixes such as Williams where higher voltage matrix was used. However, over the years, the 1N400x rectifiers have improved to the point where they will also work... even though they aren't intended for this.
I just love the search function. I was working on my Roto-target and then the target lamps stopped working. I found that some of the under-playfield diodes were open. I went to Radio-Shack and found some switching diodes. I then checked here for compatibility. I found this thread and felt safe to install them. My targets now work as they should.
I know this is a very old post but very relevant for me now. I'm restoring my first machine (a Gottlieb System 1 Sinbad) and I have found one diode on the bottom panel that is bad (see picture). Based on your original post I'm assuming but hoping someone can confirm that I can use a 1N4148 as a replacement for it Thank you in advance!