Maybe you did not know, but Ralph Baer invented the switch box at the same time he invented the video game. As a matter of fact, he thought it would be easier to build a small box to share the TV set between the game system and the antenna !
Old pong games did not use the composite input (the yellow cinch plug). They simply connected to the antenna plug of the TV set through a small switch box, which was nothing but a simple switch and a small matching transformer. As a matter of fact, television sets used two RF inputs. The normal antenna input, which used two screws, requires a 300-ohm impedance. The F-type input (the plug that screws to the TV set) requires a 75-ohm impedance. Both are not compatible, so a matching transformer is required to adapt one impedance to the other. Most of the time, you will want to convert from 300 ohms to 75 ohms.
The problem is, most pong games used a phono output plug which looked like this one:
And you were puzzled when you saw that your TV RF input connectors looked like one of these two:
There are two solutions.
The easiest is a cheap "Phono-to-F" adaptor, which can be found either at Radio
278-267) or at
AtariAge. This small adaptor contains a matching transformer and will give
slightly better quality pictures than regular switch boxes. If you want to use a
switch box for any reason, you can still buy one at Radio Shack, reference
15-1268. It also includes a matching transformer.
There are still a small number of games which used their own terminals, making regular switch boxes impossible to use with them. The Magnavox Odyssey series are a good example. The only two solutions are either to find a switch box on the Internet (eBay for example) or to cut the plug of your game cable and replace it with a male phono plug (the model which looks more like the old ones can be found at Radio Shack under the reference 274-321).
Finally, there are a few games which used a more complicated system, like a combined signal (power + video) or a composite signal to be modulated. First Dimension model FD-3000 delivered a composite signal. This one can be directly sent to the composite input of your TV set (the yellow plug). Else, you will need an RF modulator, which can be found at Radio Shack under the reference 15-2526.
If you come by a game that doesn't meet any output standard cited here, please contact me and I'll try to help as best as I can.