Strictly recording? If an Ampeg was involved, the odds are in favor of a B-15, otherwise often direct.
In the realm of guitar, there are all sorts of misconceptions…all of Zep I was a Telecaster through a small Supro combo, and while I haven’t come across any documented evidence, circumstantially I’d guess that JPJ was going through some sort of Vox rig; the solo on “Stairway” was a Tele through a Vox AC-30, the electric 12-string was a Fender. Blackmore ran his Strat through the same model on Machine Head/“Smoke..”, and used a Gibson 335 with the Vox earlier on. The blistering guitar sounds on The Stooges’ Raw Power was a LP through yet another AC-30. Hendrix would use Fender amps for clean tones in the studio, The Beatles employed a Selmer Zodiac combo, and so on.