1980 Amtrak BigBore K5LA

jjgravy
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1980 Amtrak BigBore K5LA

Postby jjgravy » Tue May 15, 2018 2:16 pm

I recently acquired this amazing former Amtrak K5LA for an absolute steal on Craigslist. It’s a true tagless manifold with unmarked 3a and 4a bells. All bells are unrestricted and reaches 120+ decibels at 250 feet at 95 psi. Bells have been sanded, buffed, and shined to bare aluminum with a powder coated grey manifold (upside down part number). I was wondering if there was a way to narrow down the year exactly? I’m almost sure it’s a 1980-81 based off my research but I have no way of being 100% sure. Any thoughts would be greatly appreciated!
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Jordan G.
Various Nathan horns, GW E-Bell

jjgravy
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Re: 1980 Amtrak BigBore K5LA

Postby jjgravy » Tue May 15, 2018 2:18 pm

Few more photos
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Jordan G.
Various Nathan horns, GW E-Bell

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railgeek
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Re: 1980 Amtrak BigBore K5LA

Postby railgeek » Tue May 15, 2018 2:45 pm

If all bells are like that second to last photo, then someone drilled them out. It might be loud, but not as nice sounding as a factory horn.
-Reed S
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jjgravy
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Re: 1980 Amtrak BigBore K5LA

Postby jjgravy » Tue May 15, 2018 3:24 pm

Jordan G.
Various Nathan horns, GW E-Bell

jjgravy
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Joined: Tue May 01, 2018 9:06 pm
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Re: 1980 Amtrak BigBore K5LA

Postby jjgravy » Tue May 15, 2018 3:27 pm

Each bell has a slightly different sized opening. None of them get smaller than a pencil eraser.
Jordan G.
Various Nathan horns, GW E-Bell

Evansville-Antiques
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Re: 1980 Amtrak BigBore K5LA

Postby Evansville-Antiques » Tue May 15, 2018 6:36 pm

those inlet holes might cause you some issues

jjgravy
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Re: 1980 Amtrak BigBore K5LA

Postby jjgravy » Tue May 15, 2018 7:21 pm

How so?
Jordan G.
Various Nathan horns, GW E-Bell

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FS150HZ
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Re: 1980 Amtrak BigBore K5LA

Postby FS150HZ » Wed May 16, 2018 7:10 am

The inlet size on the bell you photographed is about 3/8". :shock:

The standard air inlet size for a K bell is around 1/8", if not slightly less. The reason is for air efficiency, and as mentioned, musicality. The horn sounds pretty bad, and I'd imagine uses a bit more air. That being said, my understanding is 5 chime K horn manifolds are fairly restrictive, so it probably doesn't change much except the horn's responsiveness to lower pressures. It's been mentioned before that 3 chimes K's tend to outdo their 5 chime counterparts by 1-2db. The ugly sound is probably more related to the inlets being larger on the lower pitched bells. The dominance of the lower bells on that horn is ridiculous. You can barely hear the higher bells.

In terms of loudness, are you sure your measurements are correct? 120+db at 250 feet is equivalent to at least 127db at 100 feet, which is about 12-13db louder than a K5 at full locomotive pressure in an open field test at that distance. I doubt the larger inlets even made the horn much louder, if at all, because of the manifold restrictiveness. That being said, don't test any of these bells individually. All the available air would be directed into that gaping hole, which I would be surprised if it didn't destroy the diaphragms. It would be a cool experiment to see if the loudness increased drastically, but it's not something I'd like to try with a vintage horn.

It's too bad someone drilled out the inlets, as it's likely it accomplished no additional loudness, and ruined the melodic quality. Tapping the inlets, and installing set screws with 1/8" holes in them should work. Sometimes slightly (and I mean slightly) larger inlets on certain bells can improve musical quality, but only if it's done with specific knowledge in mind.

jjgravy
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Re: 1980 Amtrak BigBore K5LA

Postby jjgravy » Wed May 16, 2018 9:52 am

Thanks for your feedback! I highly disagree that it sounds “terrible” but each to his own. I personally love the lower pitches. Reminds me of the mellowness of the older M series horns. And I checked the decibel readings 3 times (once at 22 degrees, then 56, then 83) and all were about 122-31 at 250 feet. All at roughly 90-100 psi. Absolutely insane. And yes, all 3 decibel tests were recorded with all bells facing forward, not individually. That probably would be fun to try though with just one bell! Maybe if I find a broken bell or one is seriously bad shape I’ll try it some day and get back to ya on that. I believe they were drilled out in an effort to tune them “the easy way”. The smallest inlets are on the 1,2, and 5. The biggest openings are on the 3 and 4 bells. 3a bell is shown in the photo. With that being so, I can’t understand why the 1 and 2 bells are so dominant so apparently the red neck tune was a fail. Thanks for your set screw idea. I’ll definitely look into that!
Jordan G.
Various Nathan horns, GW E-Bell

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FS150HZ
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Re: 1980 Amtrak BigBore K5LA

Postby FS150HZ » Wed May 16, 2018 11:48 am

Interesting the 3A and 4A inlets are the largest, because both bells are almost inaudible. If the set screws don't work, then you know you have another issue.

Also check to make sure you have enough air going into the horn. The K5LA I had sounded similar to that when I used an air line that was too small. 1/2" air line is generally the minimum standard for horns. Depending on the wear of each bell, certain bells will hog most of the air when not enough air is getting into the manifold. If you're using a standard shop air regulator, then the regulator might be the restricting too much air flow as well.


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