Convert binary mode to text mode and the reverse option

od -An -vtx1 Check.tar > Check.txt

You need -v or od will condense sequences of identical bytes.

For the reverse:

LC_ALL=C tr -cd 0-9a-fA-F < Check.txt | xxd -r -p > Check.tar

Or:

perl -ape '$_=pack "(H2)*", @F' Check.txt > Check.tar

If your purpose is to transfer files over a channel that only supports ASCII text, then there are dedicated tools for that like uuencode:

tar cf - myfiles.* | xz | uuencode myfiles.tar.xz | that-channel 

And to recover those files on the other end:

uudecode < file.uu

would recreate myfiles.tar.xz.

Or:

uudecode -o - < file.uu | xz -d | tar xf -

To extract the files.

Answering the X part of this XY problem, I would recommend you investigate the reason your binary file transfers don't transfer properly.

If it turns out the reason is because you don't have an 8-bit clean datapath you could then use existing tools that were created to handle this situation, such as base64 or even uuencode. Old but still very effective.

tar czvf - /etc/h* | base64 >/tmp/tar.tgz.b64
ls -l /tmp/tar.tgz.b64
-rw-r--r-- 1 root root 7364 May 26 11:52 /tmp/tar.tgz.b64
...
base64 -d /tmp/tar.tgz.b64 | tar tzvf -

or

tar czvf - /etc/h* | uuencode - >/tmp/tar.tgz.uue
ls -l /tmp/tar.tgz.uue
-rw-r--r-- 1 root root 7530 May 26 11:51 /tmp/tar.tgz.uue
...
uudecode /tmp/tar.tgz.uue | tar xzvf -

In my case I didn't have xxd or uudecode on the remote device but I did have bash. I ended up with the following:

Convert from binary to txt with:

od -An -vtx1 myfile.bin > myfile.txt

Then convert back from txt to binary with:

while read p; do
    IFS=' ' read -r -a array <<< "$p" 
    for index in "${!array[@]}" 
    do
        echo -en "\x${array[index]}" 
    done
done < myfile.txt > myfile.bin