Prime Manufacturing is a company that has been in the railroad business for a long time, making all sorts of locomotive accessories. Some products that they manufacture are pneumatic bell ringers, cab mirrors, air conditioning units, and much more. Also, for a period of close to thirty years, Prime offered locomotive air horns. Union Pacific and Burlington Northern were two large customers, with the PM-920 and PM-990 respectively, and quite a few of the horns purchased by these railroads are still in service. The first Prime horns were introduced in 1972, and it wasn't until 1999 that Prime finally got out of the horn business. In that time, they sold many horns, mainly consisting of two specific models, the PM920 and PM990. Today, Prime has been purchased by the Dayton-Phoenix Group, Inc. and still manufactures many non-horn related products. In the end, Prime sold its remaining stock of horns and spare parts to one individual, a private collector. Unfortunately, Prime purged all records of their horns, including documentation, historical articles, and specifications. Thankfully, there are many collectors who have worked to save copies of as much of this literature as possible.
Designations and Chords
Bells and Notes
Over time, Prime had several different configurations that they offered. Oddly, the chords of some of these changed over time as well. It seems that Prime changed the castings on their bells twice through their history, resulting in a couple different notes for two of their bells. The casting changes represent what are known to collectors as three different generations of Prime horns. The first change occurred in 1973, only a year after production started, and the second in the early 1980s. Also, for clearance reasons, Prime cast the bottoms of their 1 and 4 bells flat instead of completely round after certain points in time. The 1 bell was flattened very early on, whereas the 4 bell was flattened early into the 3rd generation at the request of Union Pacific. Here is a chart of the Prime bells, along with the notes they played at each production date / generation, whether the bells have a flat bottom flare or not, and their Leslie bell equivalents. To the best of my knowledge, this is accurate.
NOTE: Prime never numbered their bells or used Leslie equivalent numbers. I have numbered them here for discussion purposes only, and these numbers should not be taken as Prime's bell numbering scheme. Prime only used complex part numbers to refer to their different bell sizes.
| Prime Bell |
1972 - 1973 |
1973 - mid 80s |
mid 80s - 1999 |
Leslie equivalent |
| 1 | C | C* | B* | 25 |
| 2 | D# | D# | D# | 31 |
| 3 | F# | F# | F# | 37 |
| 4 | A | A | G#*** | 44 |
| 5 | A# | A# | A# | 48 |
| 6** | C#** | C#** | C#** | 55 |
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* flare on bottom of bell flattened ** this bell was never produced *** bottom flare flattened only after the first couple years of production | ||||
Prime PM920
Using the table above, we can piece together the horns offered by Prime, and the chords that they sound. First, the most common horn was the PM920. This horn uses bells 1, 2, and 4, on a low-profile manifold. Up until the mid-80s, this horn played C, D#, A, just like it's Leslie counterpart, the S-3L. However, this then changed with the newest castings, and it then played B, D#, G#. Some transition horns in this time period were found playing Leslie's advertised S-3L chord, B, D#, A. Also, some other horns at this time played an M3-like C, D#, G# - a very pretty G# major triad. The vast majority of Prime horns produced seem to have been the 2nd generation PM920.
Prime PM990
The next most popular horn was the PM990. This horn uses bells 2, 3, and 5, and plays D#, F#, and A#, on a high-profile manifold. Just like Leslie's S-3K, it was purchased and used extensively by the Burlington Northern. Strangely, this horn was not in Prime's initial offerings, and didn't appear until a few years after production started. Also, many PM990s have a sharp high bell, producing more of a B major triad, rather than the expected D# minor chord.
Other Models
The last few horns are very rare, as only a few were produced, if any. First, a PM927 is a single-note horn, similar to Leslie's S-25, S-31, etc. I don't know if any of these were ever produced. Next, the PM928 is Prime's copy of the Leslie S-2M, using bells 2 and 4. There were very few of these produced, and I know of only one surviving example, thankfully preserved in a collection. The last offering in the Prime line was the PM929. This horn was meant to mimic a Leslie S-5T, and used bells 1, 2, 3, 4, and 6 on a low-profile 5-chime manifold, nearly identical to the manifold used by Leslie's SL-4T. Unfortunately, Prime never received an order for a PM929, and so this horn, along with their 5-chime manifold and 6 bell, were never produced.
| pm929_replica.jpg | in 2008, Jodie Wells built a PM929 replica using a Leslie manifold, and constructing a Prime "6" bell from a modified Leslie 55 bell - picture this with a low-profile manifold, and this is likely what a true PM929 would have looked like | |
| pm920_1stgen_1.wav | Ron Chamberlain's 1st generation PM920 - compare this to my dad's horn below, which is a 2nd generation PM920, and the chord is almost identical (Copyright Ron Chamberlain, used with permission) | |
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| pm920_3rdgen_s3l_1.wav | here we have a 3rd generation PM920 with what is likely a 2nd generation 4 bell, followed by a Leslie S-3L for comparison (Copyright Ron Chamberlain, used with permission) | |
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| pm920_mixedbells_1.wav | last, here is a transition horn with a second generation 1 bell and third generation 4 bell, playing G# major triad (Copyright Ron Chamberlain, used with permission) |
Construction and Generational Differences
Construction vs. Leslie SuperTyfon Horns
Prime horns are based on the S-style SuperTyfon series of horns manufactured by Leslie. In fact, all the Prime parts are interchangeable with the corresponding parts on a Leslie S-style horn. If a Prime needs new diaphragms, you can substitute a Leslie S-style diaphragm, for example. Some roads went so far as to upgrade their Prime horns with Leslie RS-style power chambers when they started to fail, extending these horns' service lives for many more years. Prime was able to market a line nearly identical to the SuperTyfon, since the 20 year patent on they SuperTyfon design had run out just as Prime's production started.
Even though Prime horns are mechanically almost identical to Leslie's SuperTyfon series, this is where most of the similarities stop; there are many differences which separate Prime apart from their competitor. Prime's horns are of a much heavier casting, for one. It seems that each part Prime made is cast with much more aluminum than the Leslie counterpart, leading to an overall heavier horn. This extra weight effects the tone of the horn as well; the heavy castings tend to give the Primes a smoother, more rich tone, than a comparable Leslie. They are more sturdy than Leslie horns as well - ever hear of a Prime bell being bent or broken because of a tree limb, like is heard on occasion with Leslie bells? Of note, though, is that Prime does appear to have used different orifice dowel sizes, similar to Leslie, though there is no rhyme or reason as to why some horns use all the same orifice dowel versus variable dowels. The variable dowels match the Leslie 2-3-3 dowel configuration of a variable S-3L. Those with all identical dowels could use the equivalent of the Leslie 2 dowel, Leslie 3 dowel, or a custom size of 0.112-inches.
One of the main visual differences in a Prime horn is that the bells have a support "rib" on each side, strengthening the bell at the base. The bells have the part number cast in the side, ahead of the rib (always a P followed by a dash and a series of numbers). Some of the later production bells have a date cast as well - I assume this is when the mold was built. Some even have additional casting numbers, for which the purpose is unknown. On the power chambers, the backs have a part number cast as well. The front of the power chamber is basically round where it meets the manifold, with six half-circle cutouts (see photos), as opposed to Leslie's narrower, "scalloped" power chamber base. Unlike Leslie bells - which could also be described as "scalloped" at the base where they join the manifold - Prime bells are completely round at the base. The manifolds are even different. The main difference is that there is no Leslie name present on the manifold, though other subtle differences can be found, such as the option for restrictor valves on later PM920 manifolds as noted below, and a bit less support "webbing" between the main trusses of the manifold (most visible on the high-profile manifold). Last, Leslie base gaskets are "scalloped" like the bell flanges to match the contours of the bell, manifold, and power chamber, and the gaskets were a paper type gasket. On the other hand, original Prime base gaskets are completely round (for obvious reasons), and are made of a very thin, somewhat stiff rubber material (though Leslie and Prime gaskets are interchangable).
Valved Manifolds and Other Accessories
Another difference in the Prime line is the inclusion of several optional accessories. One option that was somewhat common on the Union Pacific was the addition of pressure-triggered valves inside of the horn manifold (the restrictor valves noted above), introduced early into the 3rd generation. These valves were made available on both styles of three-chime manifold, though I have only seen low-profile manifolds where they were actually installed. They are located in the air passage between the middle bell and each outside bell. Manifolds that can accomodate them appear to have a wider air passage cast into the manifold near the outer bells. The theory is that if the engineer is in an urban setting, he can pull the whistle cord only half way, and the valves would keep the air stream from reaching the outer two bells - a sort of additional modulation, if you will. But when in rural country, or during an emergency when more sound is needed, the engineer could pull all the way on the whistle cord. When full pressure entered the manifold, the internal valves would open, and the horn would sound all three bells. The manifolds with built-in valves were not in Prime's first offerings, but were introduced not much after the first casting change in 1973 (see below). Union Pacific liked these valves so much that they retrofitted some of their older Primes and Leslies with the new valved manifolds, often placing the 1 or 25 bell in the center position. Missouri Pacific (MoPac) also used this manifold, and these horns became known as "MoPac Moaners".
Another offering, though not as common, was a riser, allowing low profile horns to have extra clearance. These risers basically raised the horn about three inches off the mount, while still providing ample support. While discussing manifolds, it is interesting to note that Prime catalogued five different manifolds, and each of these manifolds was built for a single horn model. This doesn't seem too odd until you consider that Prime advertised two different three-chime models. The PM920 was always sold on the low-profile manifold (similar to a Leslie low-profile manifold), which may be why risers were also offered. The PM990 was always sold on the high-profile manifold (similar to a Leslie high-profile manifold).
Three Generations of PM920s
As noted above, collectors have widely accepted the designation of "generations" when describing Prime horns. Interestingly, the only major differences between the generations affect the 1 and 4 bell, used on the PM920 and not the PM990. As such, generational talks typically deal with PM920s only. The three generations represent different castings for each of the bells, and the different chords the resulting PM920s produced. The first generation, as noted above, is signified by the rounded-flare 1 bell. There are no other major differences, and even the chord sounded is the same as second generation PM920s. This generation is called out separately because of its historical significance to the Prime line. Second generation PM920s make up the bulk of the PM920s that were sold, and as noted above, are basically the same as a first generation horn other than the 1 bell flare being flattened.
Third generation PM920s are quite a bit different, in both castings and chords. Regarding the chords, the 1 and 4 bell are a half step flatter, as indicated in the table above. Visually, there are a number of other differences, as well. First, on the 1 bell, the support ribs are wider than previous generations. On earlier horns, the ribs aren't as wide at the base of the bell, and taper out to the bell flange. On third generation bells, the ribs are the full width of the flange at the base of the bell. Next, the earliest third generation 4 bells - with round flares - are distinguishable by the presence of additional casting numbers on the bell when compared to earlier horns. Obviously later 4 bells are easy to spot, with their flattened flare on the bottom of the bell.
| pm920_2001_1.jpg | my father's PM920 - notice the flat flare on the low bell and support ribs on the sides of each bell | |
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| pm920_030614_1.wav | at Oak Ridge 2003, we blew my dad's standard second generation Prime 920 on the RS1 | |
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| pm920_030614_4.wav | later that day, Bill Williamson's PM920 with internal valves was blown - notice how the top bell starts before and stops after the two other bells |
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