1960
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Can't help you on the value--I would look for a clarinet blog or web site and ask there. The Selmer serial number chart indicates that would have been made in 1942.
The serieal number is usually found at the bottom of the upper joint. The value of your clarinet will depend on several factors, some of which include the condition of the corks and pads, is the silver worn, and had the instrument been well cared for. I suggest taking it to a dealer or instrument technician for an honest evaluation.
According to Selmer's website 1952
A Selmer trumpet with a serial number of 43417 was made in 1950, so as of 2013 it is 63 years old. All Selmer trumpets have a serial number and there is a chart that shows what year the trumpet was made.
If you mean the series number is K.... , then the clarinet is not from 1948 but from the early 1930's (a 1948 Selmer would be N....). As such it would be of interest to people who prefer early Selmers, and if in really good condition it might be worth around £500 (sterling). Personally I think the K's and L's are the best they ever made, but not everybody would agree!
I have a Selmer Flute and would like to know when it was made. The serial # is 776481.
1952
1894
a 1971 Mark VI, around $6500 in today's market
Around 1963.
Most likely 1970.