The P Series Horn

The "P" Horn

nathan airchime P5, P5A, P01235, P3, new cast, old cast, pat pending, pat pend, air horn, airhorn, railroad locomotive horn air chime

The P series horn was introduced after M horns became unpopular on railroads due to their high maintenance characteristics. P horns, unlike M horns, can have bells placed at any position on the manifold, and have common internal parts. Any of the bells can be reversed at any position on a P horn manifold. These horns don't need to be tuned, and dont have any metal to metal contact which creates wear. This means a P horn, with the normal replacement of the internal parts (rubber seat, gaskets, and diahpragm disc) which are sold as a kit, will not wear out. P horns are also very air efficient which doesn't really make a difference to a railroad, but is good for collectors with a limited air supply.
P horn bells were originally tuned to the following notes:
#1...C# (277 Hz)
#2...E (330 Hz)
#3...G (392 Hz)
#4...A (440 Hz)
#5...C# octave (554 Hz)
A P5 horn would consist of the 1, 2, 3, 4 and 5 bells, while a standard P3 has bells 1, 2 and 4. P3 horns usually come on a P5 bracket with the top two positions blanked off, but a dedicated 3 chime bracket was made and is still offered for P horns.
Deane Ellsworth, who was the "horn guy" for Amtrak came up with a new idea for the P5. He got Nathan to make a special #4 bell, which plays A# instead of A. A new P5 was born, the P5A (A = Amtrak). This had bells 1, 2, 3, 4A, and 5 and was ordered on Amtrak's first F40's 200-229, also seen on the P30-CH, and Turboliners. This was also the introduction of the low mount P bracket. A P5A will come standard with a low mount. Another type of P5 was thought of which introduced the #0 bell. The #0 bell plays low A (220 Hz), and was used in place of the #4 bell. This horn uses the 0, 1, 2, 3, and 5 bells, and also a low mount bracket. There is no official short hand for this horn, so it is referred to as a P01235, or "0 bell P5" for short. These horns were used on Amtrak's E60 locomotives, and I beleive that is their only major railroad application.

Around the mid 1970's the sound of the P horn started to change. New castings that aren't accurate came into play and resulted in most of the bells to play different notes. The 0 and 4A bells castings haven't changed, but the 1, 2, 3, 4, and 5 bells have. However, the #4 bell is the only one to still play the same note. The main visible differences are that the older cast bells say "PAT PENDING" near the foot of the bell, and the newer castings are abbreviated "PAT. PEND.". The flare of the bells are also different, but that is hard to notice unless you have both styles infront of you.
The new casting notes of the P horn are:
#1...D (292 Hz)
#2...F (330 Hz)
#3...G# (415 Hz)
#5...C (523 Hz)

Work's Cited: Fred Berry's "The P-Unit Primer" - Horn & Whistle Magazine

P5 (From the Central NY NRHS's E8 #808) sporting home-made bug covers