Headphones+Quad 606

Hello,

I have a set of Quad pre/power amps 606 series,
and there is no headphone jack in the pre-amp.
I was wandering... is there a way to add such a feature
on it? What do I have to do? Add something to the pre-amp box? Buy some device which connects to it? or
I need a new pre-amp?!

Thanks in advance.