Not quite vintage but this amp from Audiolab, the 8000 LX sounds fantastic with my Sennheiser HD600. Even though I also use the Bottlehead Crack, I still prefer this amp with the Sennheisers. The amp drives them with authority and makes them sound clean and detailed.
I am building a vintage system for the lounge primarily for headphone use and have just snagged a Trio Kenwood KA-5700 amp. Hope it sounds as good as the Audiolab.
My first vintage amp was the KA-5700.................still have it in my home office and still love it. Had blue LED's put in it.....................great little amp!