Acid flux is actually very aggressive stuff and more forgiving of poor cleaning. Rosin flux is always used in electrical work, and is very important n electronic work. Acid flux is so aggressive it can eat the thin layers of copper used to make printed circuit boards, and the salt residues it leaves behind are conductive if they get moist (and since they are hygroscopic they tend to stay moist). The rosin fluxes have different levels of 'activation' that indicate how aggressive they are. Some of the finest geometry printed boards use immersion gold plating (a few micro-inches thick) and can use the least aggressive fluxes. The carrier for the flux can be petroleum based or water based (actually just not petroleum so it cleans up with water), but the actual active component remains the same. The electronic industry has been moving to water cleanup and low activity fluxes for many years, particularly after 1,1,1-trichloroethane was pretty much banned as a board cleaner. Just about everyone had a vapor phase degreaser, a tank that held hot vaporized 1,1,1. When a cool object (room temperature) was placed in the vapor it condensed on the object and dripped off cleaning the item. Now glorified dishwashers are used. By measuring the conductance of the wash water you can tell if the items have been cleaned of ionic contaminants. Really pure water is a very good insulator.

First make sure the water is turned off and the line drained. Next put on a pair of leather work gloves and have a fairly large cotton rag handy (an old Tee shirt is perfect). If your right handed hold your torch in your left hand as near the wall as you can with the torch tip and flame pointing out towards the valve and away from the wall and have a pair of channel locks in your right hand. Heat the valve and try turning it with the plyers, as soon as it will turn give if a twist and pull outward and the valve will slide off the pipe. Lay the valve aside, but don't forget, it is hot, you should have some corrugated cardboard or a bucket to drop it in so it won't burn the cabinet or floor covering. now grab the cotton rag in your right hand and reheat the end of the pipe till the remaining solder melts, remove the heat and grab the pipe with the cotton rag and pull towards the end of the pipe, that should remove the excess solder leaving just a light film on the copper as if its silver plated. If not, repeat the heating and wiping a second time. Now set all that aside and let the pipe cool then take a1-1/2" wide strip of emery paper about 6" or 8" long and loop it over the end of the pipe and pull the emery back & forth like a shoe shine rag from two or three directions to insure the excess solder is cleaned off. Now get a compression type angle stop valve, Slip the compression nut on the pipe, then slide the compressing ferrule on the pipe. Now slip the new valve on the pipe as far as it will go, then slide the compression nut ahead to the valve and tighten the nut. You need two tools to properly tighten the nut, once wrench to hold the valve steady while you tighten the nut with a second wrench. Note.... the fixture stub out is normally 1/2" copper pipe. Compression fittings are primarily used on copper tubing so they are generally listed by "tube size". Pipe is measure by the OD while tube is measure by the ID so when selecting a new compression type angle stop look for one that says 1/2" copper pipe or 5/8" tubing, they are both the same size and will fit your stubout.

Well, ...what kind of soldering? There is the soft, low heat soldering which is done in copper piping, electronics, etc. or the high strengths silver soldering which is done with high heat. That pin your'e talking about looks like needs silver soldering to make it strong. Cleanliness is of importance, always clean so metal is showing and the use of flux, high heat oxy/acetylene torch is a must have, the solder melts when you see metal just slightly get red.

I do not think this is a toy, but is a model for display. There are a few distinctive details: 1. Vertical steering column and on the right side. 2. Has a squeeze bulb horn. 3. Emulates wood spoke wheels. 4. Model style is a run-about. 5. Has a folding cloth top styled after those used on small buggies. 6. The radiator shape is distinctive and may help identify the model.7. Its not a Ford. Old Fords had 3 pedals on the floor. This one has an apparent gear selector lever. 8. There is a design embossed on the running board that may also be on the full size car. It is possible this is merely a display item that was not modeled after any particular car. However, I get an impression this is a model of a real car and has accurate scale.