Powerage has come to occupy such a huge place in AC/DC mythology that it's hard to look at it dispassionately. It's Keith Richards' favourite AC/DC album; when Axl Rose replaced Brian Johnson in the band, two tracks from it – 'Riff Raff' and 'Rock 'N' Roll Damnation' – suddenly appeared in the live setlist; it's the one the hardest, corest of hardcore fans always go on about, Even within the AC/DC camp, it appears to have a special status, albeit one that might baffle non-converts.

"After we'd done Let There Be Rock, Powerage was probably us experimenting a little bit," Angus Young told me in 2014. "My brother George said: 'Your first album and your second album, these are a lot of songs you've had for years, and you've worked on them and refined on them, so when you hear them you go: That's a band playing that.' And that's what he wanted for Powerage. That's about the closest we ever got to an experiment." Mark Opitz, who engineered the album, told the writer Jesse Fink: "In a way it was AC/DC's Sgt Pepper's."

Truth be told, while I love AC/DC – and Powerage is, I think, by a distance the best of their albums – it's hard not to see that without wondering what on earth Young and Opitz are on about. Experimental? You'll look long and hard for extended modal electronica interludes, and you won't find any. Their Sgt Pepper's? There's no framing device, no sitars, no psychedelic whimsy. And yet, and yet, and yet …

And yet there's some germ of truth in what they say. Powerage is the most extreme AC/DC record. It's the least flashy, the most gritty, the least concerned with its audience, and the driest: one wouldn't be in the least surprised to be told Steve Albini had spent his entire career as an engineer/producer/recorder trying to capture its sound. It's also the first AC/DC album to dispense with bluesy shuffles: everything here is four-to-the-floor. Most of all, it's extreme in its lyrics. Hitherto, Bon Scott's writing had often been a strange alternation between seaside postcard bawdiness and almost psychopathic malevolence. On Powerage he stripped away the bawdiness, and reined in the malevolence: he seems more like an observer than a participant. Powerage is by some distance his best lyric set, one that reads like Jim Thompson short stories set to music. Crucially – I've made this point before, but it bears repeating: Powerage is the only AC/DC album entirely free of sexual innuendo. On 'Gone Shootin'' there's even a woman entirely free of sexual desire, who wants only oblivion. As Scott puts it', with equal parts disgust and empathy, in the most economical description of the squalor of addiction ever set to record: "I stirred my coffee with the same spoon."

The result was an album that seethes with barely controlled aggression. Which, Fink writes in his book The Youngs, was what George Young – Malcolm and Angus's older brother, and the album's co-producer with Harry Vanda – had wanted, stirring the group into antagonism. Fink also notes that the band were having a hard time in Australia, which had not embraced Let There Be Rock, and that further fed into the album's bleak mood.

It's the bleakness that makes Powerage. Without the triptych of 'Down Payment Blues', 'Gimme A Bullet' and 'What's Next To The Moon', the more triumphant tracks (though it's all relative, here) wouldn't cut through the fog. While 'Riff Raff' and 'Sin City' might be a good bit more downbeat than the centrepiece tracks of the previous album ('Let There Be Rock' and 'Whole Lotta Rosie'), they serve the purpose of breaking the tension: their original positions at the end of side one and the start of side two of the vinyl album as a buffer between the runs of unmitigated misery.

While 'Down Payment Blues' is the emotional heart of Powerage, the one where its central message – life is shit, poverty is shit, and what's the point of it all? – is laid out in full, 'What's Next To The Moon' is the album's strangest and most compelling track, the one where the claims that Powerage is experimental bear the most truth. It's an oddity both musically and lyrically: it's a song so stripped back it's barely there. Rather than basing it around a colossal riff, the verses are carried on a simple, single guitar phrase over muted bass and drums; the choruses do not release the tension: that only comes after Scott howls out the title, and the whole band unwinds. While AC/DC had long since mastered the building of tension, and coiling songs like springs – 'Live Wire', 'She's Got Balls', 'Dog Eat Dog' and 'Hell Ain't a Bad Place to Be' are based to varying degrees on that technique – they'd never done so with such discipline as here ('Riff Raff', another explosion of released tension is rather different, in that the 90 seconds of intro are all tension, the body of the song is all ecstatic release; there's no build and release and build and release).

The tension is ratcheted up by Scott's lyric. He was usually a gratifyingly direct lyricist: the furthest he might go to metaphor was innuendo. On 'What's Next To The Moon', however, he produced something startling and allusive, mixing references to silent movies ("I tied my baby to the railroad track") and superheroes ("Heavenly body flying across the sky / Superman was out of town") in a revenge fantasy that ends with the narrator facing the brutal consequences of capture ("Hitting me with the third degree / Working on a thumbscrew"). It's perhaps the strangest song – missteps like 'Love Song' aside – in the AC/DC catalogue, and all the better for it.

Needless to say, when AC/DC handed in Powerage to Atlantic, the label didn't hear a hit single, and this was meant to be the point at which the band started producing hit singles. But the album was already at the point of production, so the European version of the album was released without said single, and a track called 'Cold Hearted Man' (which was on my copy of Powerage, the first album I ever bought) until it could be substituted for 'Rock 'N' Roll Damnation', which duly became the hit. In truth, it's not all that much of a song – it's messy and old-fashioned compared to the rest of the album, with a riff that's barely evolved from the boogie of their earliest recordings. But by God, did Vanda and Young throw everything at it to make it a hit. As Mark Opitz told Fink: "You can hear Vanda and Young in 'Rock 'N' Roll Damnation'. The hooks. Shakers coming in. Tambourine to get the groove. Which if you notice is just like [John-Paul Young's] 'Love Is In The Air'. They were very big on lots of Motown tricks."

Powerage proved to be the end of one road for AC/DC. The hit single secured, the pressure was on to go to the next level. That meant George Young and Harry Vanda stepping aside as producers, to be replaced by first Eddie Kramer and then, of course, Mutt Lange. It meant them sacking their manager, Michael Browning. Atlantic felt Powerage was too hard for US radio, which was where the label wanted the band to be, and Malcolm and Angus Young were perfectly willing to shake up everything surrounding the band to become the biggest rock band in the world.

Sales figures tell us they were right to do so. It's hard, too, to argue that Highway To Hell and Back In Black were anything other than great albums. But it's telling, too, that when a band comes along that wants to capture the sound of AC/DC – bands like Airbourne or Rhino Bucket – it's not Back In Black they try to recreate; instead it's usually as if they're trying to make the album AC/DC might have made between Powerage and Highway To Hell, where the sound and toughness of the former meets the accessibility of the latter. Powerage, still, is peerless.