I’ve got a good question here, how do you tell the difference between the 3 generations of k5hl and k5lla Nathan horns? I know there is a slight sound difference but is that it?
That’s a good question!
One for the Techy’s on here DBO or e2e.
Not sure how you define 3 generations. Aging the horns is difficult I think because parts are readily interchangeable on the K series and many in railroad life would have had some bits and pieces swapped around.
There’s some clues to be had when looking at the 30109 casting mark on the back cap. If the 30109 has large “O” for zero’s, the horn was probably produced in the 80’s, because after that the font changed to a narrower “0”.
If the horn is tagged or hasn’t had parts swapped I think the tag is still your best bet for telling the history of the horns.
The old K series Airchimes were sand cast, not die-cast. The early production K5’s which were shipped to Chessie are called “Big Tag” horns because of their large black tag (1976-77 Era).
In the mid 90’s to early 2000’s, Nathan tags were square edged and after that (up to present era) the tag corners were rounded. Then there’s the “Over the Road” edition (also rounded tag).
That’s about all I know. I’m sure there’s some guys on the Horn & Whistle board who can tell you more.
I noticed that on the bnsf GE units in the 5000 series were equipped with 1st Gen K5HLs. The 2nd Gen was on the early 7000 series and 3rd Gen is common on the 8000 numbers (mostly ES44C4’s) I found this info out on YouTube
The earliest horns were produced with a two-piece sand-cast 1L bell, and no raised letter bells. This is especially prominent in the K5HL as 3 of the 5 bells did not play the advertised note. Early ones play C, E (around halfway between D# and E), G, B, C. In the summer of 2007, they switched to the current manufacturing method with a one-piece 1L bell, and all other raised letter bells. These horns produce the “correct” notes: C, D#, F#, A, C. The newest horns seem to vary in pitch more than the older castings. The K5LLA was produced in the same fashion as the K5HL with different bells. The main tone difference is the change to using the raised-letter bells and the two-piece 1L on pre-2007 horns.
The K5LLA did not change as dramatically as the K5HL did with the manufacturing changes. Newer K5LLAs seem to have a more dominant 1L bell, but roughly play the same notes.
Another interesting note on the K5HL is that the #1 bell plays a big part in the tone of early 'HLs. The ones that play closest to E will sound better than ones that play closer to D#. Raised letter bells almost always play D#
In my opinion, the whole “generation” thing with these horns is clouded in misinformation: there only seems to be two major differences in these horns, so I don’t know how the ‘3 different generations’ got started.
Hope this helps! 
:d:d:d