Nathan P5a

Horn and two photos courtesy Brent Lee.

P5a is shorthand for the designation P1234a5. The horn uses the new, low profile P-manifold, which moves the two horn bells previously mounted under the manifold up to the sides. The horn is sometimes informally referred to as a "PL5a" to reflect this. The first picture below illustrates that the back caps are not all in the same vertical plane, as they were on the original P5 manifold.

Other views (click thumbnails for larger images):
The P5a was developed in 1975 at the suggestion of Deane Ellsworth, who had recently moved from Chessie to Amtrak and was eager to find a horn to replace the Leslie SL-4T used on the railroad's SDP40F locomotives. The P5a used a special #4a bell tuned to A# to produce a pleasing C# diminished chord, the same chord Bob Swanson originally had in mind for the M5. The P5a was used on Amtrak's P30CH locomotives, the turbo trains, and the first order of F40PH's (200-229) before it, in turn, was displaced by the K5LA.
Amtrak 229, the last Amtrak F40PH delivered new with a P5a, models a horn with optional screen cones to keep insects and foreign matter out. As with the standard P5's, the use of newer, out of tune horn bells has resulted in a number of dischordant, unmusical P5a's. This particular horn is the one heard on samples 2 and 3 under "When Bad Things Happen to Good Horns" below.
Chicago commuter railroad Metra is another large user of the P5a. Most of their horns have the 4a bell reversed.

Factory tuning was: C# diminished (C#,E,G,A#,C#).

The horn used the P-series #1, 2, 3, 4a, and 5 bells.

P5a's can still be heard occasionally on Amtrak, though their numbers are dwindling as the early F40PH's are retired. The P5a also appears on most Metra F40PH's, and occasionally on Norfolk Southern (ex-Southern) locomotives.

P5a sound samples:

Amtrak F40PH, first order (#200-229):
Sample 1...150kB...9 seconds
Sample 2...150kB...9 seconds
Sample 3...247kB...15 seconds
Sample 4...263kB...16 seconds
Sample 5...200kB...12 seconds

When bad things happen to good horns:

Amtrak F40PH's with fouled P5a's, and/or "new castings" bells:
Sample 1...103kB...6 seconds
Sample 2...158kB...10 seconds
Sample 3...95kB...6 seconds
Sample 4...154kB...9 seconds
Sample 5...220kB...14 seconds
Sample 6...134kB...8 seconds
Sample 7...64kB...4 seconds
Sample 8...185kB...11 seconds
(courtesy David Safdy):
Sample 9...401kB...25 seconds

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