Note that tr/// supports ranges, so this works too: tr|\0-9|A-Za-z|

(IIRC this might not work on systems that aren't ASCII based; perlebcdic)

Update: You said "the first 52 bytes of a character map", but \0-9 is the first 58 bytes. So maybe you want to do tr/\0-3/A-Za-z/? Or only the nonprintable characters with tr/\0-\x1F/A-Za-f/?

Update 2: WebPerl live demo of the following:

use warnings;
use strict;

print join("   ","  ",map {sprintf "%X.",$_} 0..7), "\n";
for my $l (0..15) {
    printf ".%X", $l;
    for my $c ( map { chr( $l|($_<<4) ) } 0..7 ) {
        #$c =~ tr/\0-9/A-Za-z/;   # doesn't work correctly!
        #$c =~ tr/\0-3/A-Za-z/;   # option 1
        $c =~ tr/\0-\x1F/A-Za-f/; # option 2
        print "   $c ";
    }
    print "\n";
}

__END__

     0.   1.   2.   3.   4.   5.   6.   7.
.0   A    Q         0    @    P    `    p 
.1   B    R    !    1    A    Q    a    q 
.2   C    S    "    2    B    R    b    r 
.3   D    T    #    3    C    S    c    s 
.4   E    U    $    4    D    T    d    t 
.5   F    V    %    5    E    U    e    u 
.6   G    W    &    6    F    V    f    v 
.7   H    X    '    7    G    W    g    w 
.8   I    Y    (    8    H    X    h    x 
.9   J    Z    )    9    I    Y    i    y 
.A   K    a    *    :    J    Z    j    z 
.B   L    b    +    ;    K    [    k    { 
.C   M    c    ,    <    L    \    l    | 
.D   N    d    -    =    M    ]    m    } 
.E   O    e    .    >    N    ^    n    ~ 
.F   P    f    /    ?    O    _    o    
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