Obtain Unicode encoded byte value from a Unicode character

I have read in many places that if we want to retrieve the encoded byte value from a Unicode character that you should do the following.  I'm doing everything in Powershell ISE as it has better character support.  Same problems exist in a powershell console.

[byte][char]'a'

Which outputs "97" which is 0x61 in Hex, which is the correct value.  That's great.

Now if I do the following for a different character, in this case "€"

[byte][char]'€'

Cannot convert value "€" to type "System.Byte". Error: "Value was either too large or too small for an unsigned byte."At line:4 char:1+ [byte][char]'€'+ ~~~~~~~~~~~~~~~    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException    + FullyQualifiedErrorId : InvalidCastIConvertible

So now let's try using [int16], which is bigger

[Int16][char]'€' 

It returns "8364", which is not correct.  It should return "128" as the hex code for "€" is "0x80".

How can I get my powershell to retrieve the correct character codes for some characters?