An amp head w/ its own tremolo pedal. From a blog post on 2009/10/20, while talking about one of his Gish-era guitars:

I've started using more old-school amplification, like my 1969 Marshall Super Tremolo head (currently ailing) so guitars with this kind of cut are what I'm looking for. It makes me laugh that I'm sort of back to where I started when it comes to gain and attack.

Also mentioned by Billy on twitter on 2011/06/25 while going through various guitar/amp rigs for Oceania, as recommended by "the German virtuoso Uli Jon Roth".
[Marshall wiki]

Mentioned again in an 'Oceania track-by-track' interview in 2012: "With a song like [Quasar], I know we were using a combination of a Marshall Super Tremolo amp with four rhythm guitars, and the other guitars went through a Reeves Custom Jimmy head, which is the re-creation of Jimmy Page's Led Zeppelin I amp. It's incredible."