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looks like a Conn Fiberglass Sousaphone but the braces are just very plain as compared to my big short action fiber sousa.

I don't see any mention of "L" in the Conn serial numbers but the serial number does look like it has the prefix L.
Serial L29083 ca 1983

Bell 24”
Bell collar 6”

Although the horn looks very rough the valves look great. Hope I can find a receiver.
1 valve button is missing as well. Any info toward parts or make and play-a-bility will be great.

Walking gigs - under $100 -this horn

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Ya... as Jose said. It's a 36K. Go here for the serial number translation. See the letter explanation at the bottom of the page.

http://www.horn-u-copia.net/serial/Connlist.html

Fred is a good generic name for a good generic sousaphone.