P series horns were created as a "filler" model by Robert Swanson. They were the result of his work from the T series horns and were intended to be used as a cheap, low-maintenance alternative to the M series horns until he completed work on the K series horns. The K series was to be Swanson's final evolutionary step in horn construction. To get to the P series, Mr. Swanson started with a truck horn and modified it so it would be appropriate for railroad use. It was introduced in 1953 and could be ordered in single, three, and five note models. However, Swanson did not like the product at all, and so AirChime never manufactured the P series. In fact, it was rumored that Swanson "jokingly" stated that the "P" stood for "piss-poor"; it actually stands for "pre-set pitch".

Even though AirChime never marketed the P series of horns, Nathan licensed the design, and has been selling them since 1953. While Swanson did not like the P series, they performed their intended function perfectly. Railroads did not like the fact that M horns required separate replacement parts for each bell. Even moreso, the railroads hated having to adjust the M horns every six to twelve months. The P series fixed both these problems, and allowed Nathan to compete directly with Leslie's SuperTyfon series of horns. All the internal parts on the P horns are interchangeable between bells, and since the back cap bolts in place, it is pre-adjusted and never requires voicing. Today, the P series can still be purchased from Nathan; Norfolk Southern is a heavy user of the P5 horn, for instance.

In 1976, Deane Ellsworth, who was working with Amtrak at the time, worked with Nathan to produce a new model of P horn. This horn became known as the P5a, with the 'a' for Amtrak tuning. The original P5 blew A major 7th (C# E G A C#), whereas the new P5a blew C# diminished (C# E G A# C#). This was accomplished by shortening the 4 bell to play A# instead of A. The new 4 bell is marked as a 4a bell. When the P5a was being developed, Nathan sent Mr. Ellsworth a 4 bell with an adjustable-length throat! The correct length was set, and the specs were then sent to Nathan, who cast this new 4a bell. This adjustable 4 bell, the first 4a bell, has been preserved in the collection of Brent Lee.

In 1977, a major change hit the P-series horn line. Nathan contracted out to at least two other foundries to cast their P horn bells. When this was done, new castings were created for the P horns, which unfortunately did not remain true to the AirChime specs. The new bells had different throat lengths and flares, and so the pitches on the bells were different, even though the lengths of the bells are identical! The 1, 2, and 3 bell sound approximately a half-step too high, and the 5 bell sounds a half step too low. The rest of the bells remain unchanged in pitch. The resulting "new cast" P5s play D F G# A C, which is no distinguishable musical chord.

		p5_weiler_1.wav	a P5 with old-casting bells (Copyright Norman Weiler, used with permission)
		p5a_030614_3.wav	Dennis McCurry's P5A, also with old-casting bells, blown at Oak Ridge 2003

three generations of P horns

When the P series of horns were first introduced by Nathan in 1953, they used a phosphor-bronze diaphragm disk. Also, the orifice opened up into a fairly wide, oval-shaped hole in the horn's internal chamber. Within the first year or two of construction, the diaphragms were switched to stainless steel, and the orifice opening changed from an oval shape to a completely round shape. The first series of P horns with the phosphor-bronze diaphragms and oval inlet are said to be "first generation" P horns. The replacements with stainless diaphragms and circular inlets are considered "second generation" horns. Though they differ slightly internally, the sound of first and second generation horns is basically the same, with first generation horns sounding just a little more mellow.

As stated above, in late 1977, Nathan changed the castings for their P horns, changing the pitch of the 1, 2, 3, and 5 bells. These newer castings are considered "third generation" horns. Also, another classification commonly heard is "old-cast" and "new-cast". Basically, old-cast horns are synonymous to both first and second generation horns, and new-cast horns are the same as third generation horns.

There are three main visual differences between old-cast and new-cast horns. First, old-cast horns have "Pat. Pending" cast into the foot of the bell, whereas new-cast horns just have "Pat. Pend." cast. (0, 4, and 4A bells retained "Pat. Pending" several years after 1977 before "Pat. Pend." started appearing. This is the only real change to the 0, 4, and 4a bells, as they remain true to their intended shape and tuning.) The second visual difference is the flare of the bell. Since it is the flare that determines the pitch, a trained eye can notice differences between old and new-cast P horn bells. The last difference really isn't an old-cast vs. new-cast difference, but worth noting anyway. Sometime just prior to 1977, Nathan changed the casting for its back caps. The older style of back cap has "Nathan" cast twice, whereas the newer style only has "Nathan" cast once.

		p5_2001_9.jpg	a close-up of the "Pat. Pending" casting on first and second generation P horns
		p3_030614_1.wav	a standard second generation P3
		p3_nc_020622_2.wav	... and a third generation P3
		p5_011031_1.wav	my standard P5 with old-casting bells (second generation)
		p5_nc_030614_2.wav	a P5 with new-casting bells blown at Oak Ridge 2003 (third generation) - note the loss of musical qualities to the horn

construction

A P horn is similar in appearance to the K series. The bells and diaphragm housings are of one-piece construction, and have a back cap that bolts on to the diaphragm housing. These complete units then bolt in place onto a common manifold. Also, the diaphragm housings are all of equal size, unlike M horns. However, P horns are longer, have a narrower throat, and have smaller diaphragm housings than K horns. In addition, P horns have "Nathan AirChime" cast into a raised rectangle on both sides of each bell.

Inside of a P horn, the construction is completely different from the K series. The air orifice opens up to the bottom of the inside chamber of the horn and does not use a diffuser to better distribute the incoming air stream. Also, the P horn uses a single stainless diaphragm. (On most of the newer P horns, there is a double diaphragm, though this is not required.) The diaphragm is cushioned on the outer edges by rubber gaskets, and so the aluminum housing and back cap will not wear over time, unlike their older brother, the M series. There is a rubber gasket covering the nozzle as well, held in place by a spring. Because of this, the nozzle will also never wear with use. This construction means that the P series of horns will function for many, many years, with the only maintenance required being to replace diaphragms and rubber gaskets when worn. The service life of a P horn is so long in fact that I know of several P horns that have been in constant service for over thirty years and have had no maintenance to date. These horns still sound exactly as they are supposed to sound!

P horns were very commonly sold with restrictors in the base. Restrictors are basically hex socket plugs drilled to a specified diameter. Depending on the diameter of the drilled hole, different "chokes" can be applied to the P horn, mellowing out the tone. While restrictors were available on M, K, and P horns, they seem to be most commonly applied to the P series. Common restrictor sizes are 5/32" for P3s and P5s, and 7/32" also for P5s.

p5_2001_7.jpg

a photo showing the fitting of the bells on the manifold

designations

A P horn is classified by the letter P followed by the number of the bells used in the horn. If any bells are reversed, an R precedes the reversed bells. Therefore, a P5 is not really a 5-chime horn, though we reference them as such as shorthand. A P5 is really a single-note P horn using the 5 bell. A true P5 is correctly designated a P12345, and a P5a is correctly referred to as a P1234a5. With bells 2 and 4 reversed (a common reversal), the horns are a P135R24 and P135R24a, respectively. P124s - commonly referred to as P3s - were available as well, both on the five-chime manifold with "blanks" installed on the ports with no bells, or on a special three-chime manifold. Single-bell P horns were available on a single-bell manifold.

The five-chime manifold typically has two bells mounted above each other on each side of one center bell, and is referred to as a "gull-wing" manifold due to its shape. The order of the bells on the manifold is not critical. On occasion, you will see a P12345L, or P5L for short. Though not an official designation, this refers to the P12345 on a newer, low-profile manifold introduced in 1976. This low-profile manifold originally consisted of the three-chime manifold with two "extenders" used to mount the additional two bells. To keep the horn as compact as possible, the two end positions and the center position are about an inch forward from the last two horn positions, allowing closer placement of the bells without the diaphragm housings coming into contact with each other. Newer P12345Ls consist of a one-piece low-profile manifold looking identical to the first three-piece low-profile manifolds.

Not talked about yet is the 0 bell. This bell plays low A, an octave below the 4 bell, and has remained unchanged after Nathan switched foundries, with the exception of "Pat. Pend." now cast instead of "Pat. Pending". Nathan offered the P01345 configuration, also tuned to A major 7th, though very few railroads are known to have purchased this horn. In 1976, Don Tead worked with Nathan to sell the P01235 horn to Amtrak for use on it's E60CH locomotives. Also tuned to A major 7th, this horn has a very pleasing tone, and, like the P01345, makes a very effective warning as it sports a range of over an octave. Unfortunately, Amtrak's E60CHs are the only known applications of the P01235.

		p5a_020622_1.wav	Matt Donnelly blowing his P1234a5 up at Elwood's place
		brw752_020721_1.wav	another second generation P124, in active passenger service
		p01235_warrick_1.wav	a P01235 in active Amtrak service on an E60 (Copyright John Warrick, used with permission)

last updated 02.17.2004