I made wrong, but I'm confused with that link what you wrote.
This works but not the first 50 char
echo JHTML::_('content.prepare',preg_replace('#.*<hr *id="system-readmore" */>#is','',$this->row->product_description));
Or this works too
<?php echo preg_replace('#<hr *id="system-readmore" */>.*#is','',$this->row->product_description); ?>
But this not work
echo substr(JHTML::_('content.prepare',preg_replace('#<hr *id="system-readmore" */>#i','',$this->element->product_description)),0,50);
I need your help to modify the first two to display only the first 50 char.