@SteveH posted:I'm surprised no one has mentioned using parallel diode ladders and/or bridge rectifiers to drop the voltage yet. @Hippieroofer, if you're not in a hurry for your answer, you may want to wait a day or two to see what other less expensive and simple options are suggested, before ordering something.
You're right. Any discussion about O-gauge AC voltage adjustment should include a cameo appearance by the diode/bridge dropping method. There have been many OGR threads about this. Here's a photo of the method from this OGR thread.
The math or electrical analysis of what's going on can be a bit intimidating so there is a certain leap-of-faith. The method does work but does involve soldering or equivalent component-level fussing and mussing. Each bridge component can be configured to lower the AC voltage about 1.4V. So in your case, going from 16V AC down to 9V AC would require a 7V drop...or 5 bridge rectifiers (only 4 are shown in photo). As shown, bridge rectifiers are inexpensive but the one shown in photo is eBay-Asia so with all those ships sitting off the Long Beach port...you may be cooling your heals for quite a while! Amazon prices are higher...for example:
It should be pointed out that the bridge method retains the AC character of the voltage. So you have AC in and AC out.
The thing is, when driving a light bulb, DC is just fine. So the AC-to-DC converter module suggested earlier should do the trick.
However, if I might make a suggestion, and I realize it's a bit more out-of-pocket (though you get 2 pieces) but I'd get a so-called "buck" converter module as shown above. These modules are more electrically efficient than the so-called "LM317" modules. The electrical analysis can get a bit nerdy, but one way to think of it is the "buck" converters are digital and the "LM317" converters are analog. This is a bit of semantic gymnastics but so be it.
In both cases you need a tiny jeweler type screwdriver to adjust the output voltage. But no soldering is required as both modules have screw-terminal inputs and outputs.
