The P model horn is a very simple, yet very robust model. The design is a modified truck horn design, adapted for railway use. The horn consists of a bell with integral mounting foot, diaphragm housing, nozzle, and orifice. However, there is no diffuser, and only a single diaphragm disk. (Though later models include a pair of disks, this is not needed.) What makes the P series so robust is that the diaphragm rests completely against rubber gaskets, and even the nozzle has a gasket covering its face. Because of this, the only parts that can ever wear on a P horn are the gaskets, and less often, the diaphragm.

When assembling the horn, place the nozzle gasket on the nozzle, and use the spring provided to secure the nozzle gasket in place. Next, place the smaller of the remaining two gaskets in the outer edge of the diaphragm housing on the bell. On top of this, place the diaphragm, and then the larger gasket. Once in place, attach the back cap using the six screws which thread into the diaphragm housing. To be prototypic, a P horn uses slotted screws and star-style lock washers.

tips

There isn't much that needs to be worked on with a P horn. If there are problems, usually opening the back caps and cleaning or replacing worn gaskets or diaphragms will solve the problem. If a diaphragm is cracked, it must be replaced. The same goes for dry rotted or torn gaskets. Amazingly enough, the horn may still sound with these bad parts, but it's best to replace them before any real damage occurs.

other experiments

Because of the many different P bells offered by Nathan over the years, many people have come up with some very pretty chords for the P horn. There are 11 differently pitched P horn bells, which can be combined in countless ways. The notes possible are A, C#, D, E, F, G, G#, A, A#, C, C#. They are played by the following bells, respectively (OC = "old cast", or 1st/2nd generation, and NC = "new cast", or 3rd generation): 0, OC 1, NC 1, OC 2, NC 2, OC 3, NC 3, 4, 4A, NC 5, OC 5. Try putting some new chords together and have some fun!

Another experiment carried out by many, is the varying of diaphragms. For starters, older P horns use a single disk, where new horns use a double-disk diaphragm. The double-disk tends to lessen the characteristic "chiff" when a P horn first starts, as well as loudening the horn somewhat. Also, a thicker diaphragm can have the same effect, but even moreso. A stock P diaphragm is 0.008" thick stainless steel, though I'm aware of some who have tried as thick as 0.025". These diaphragms change the tone of the horn significantly. Another modification is the use of phosphor bronze diaphragms, again in varying thicknesses. From the experiments I've heard, as thicker bronze diaphragms are used, the more mellow the sound of the horn.