Using redirection within the script produces a unicode output. How to emit single-byte ASCII text?

I am using Sandcastle Helpfile Builder to produce a helpfile (.chm). The project is a .shfbproj file, which is XML format, works with msbuild.

I want to automatically update the Footer text that appears in the generated .chm file. I use this snippet:

$newFooter = "<FooterText>MyProduct v1.2.3.4</FooterText>";

get-content  -Encoding ASCII $projFile.FullName | 
    %{$_ -replace '<FooterText>(.+)</FooterText>', $newFooter } > $TmpFile

move-item $TmpFile $projFile.FullName -force

The output directed to the $TmpFile is always a multi-byte string. But I don't want that. How do I set the encoding of the output to ASCII?