Ampex Model 351
A professional mono recorder whose tube electronics were prized enough that a plug-in developer modeled them decades later.
Overview
The Ampex Model 351 turns up in the strangest places. In the classified pages of DB (April 1971, p.25), a studio clearance sale listed two Ampex Model 351 recorders alongside the usual console gear — machines being cleared out as the multi-track era pushed them aside. And in Electronic Musician, a reviewer noted that Waves' Kramer Master Tape plug-in was built to model a hybrid machine combining an Ampex Model 350's quarter-inch transport with Model 351 tube electronics. When software designers go hunting for "the sound," they land on circuits like this one. That tells you most of what you need to know about why collectors still chase the 351.
The 351 is a tube-type mono recorder, full-track, and it was built to live in a console. That much is confirmed by the period classifieds: a Birmingham, Alabama seller offered one "in console, Full Track. Excellent Condition" for $1,150, and a Hollywood ad described a Model 300 deck fitted with Model 351 electronics in an enclosure at $1,950 — evidence that the electronics package was considered the valuable half of the machine, worth transplanting onto a different transport. Broadcast shops kept them running for years; a Texas service listing in the trade press advertised Ampex-authorized sales and service with head rebuilding available, the kind of infrastructure that only exists around gear people actually depend on.
What made the 351 worth servicing was the front end. The tube electronics are the specific thing later engineers tried to replicate in software, and the plug-in documentation is unusually precise about what that circuit does: it "broadens" midrange frequencies in a way EQ can't, fattening thin-sounding sources. That's the 351's contribution to the hybrid recorder the plug-in modeled — the transport came from a 350, but the character came from the 351's tubes. For a mono machine, that's a remarkable legacy.
A word on the name, because it confuses people. The Model 351 appears both as a standalone console recorder and as an electronics package paired with other Ampex transports — the classifieds show both configurations trading hands in the same era. Buyers should confirm which they're getting. A "351" advertised at a bargain price may be the electronics alone, or a 300-series deck wearing 351 amps, and the difference matters enormously to both value and restoration.
The machine's working life is well documented in the trade press of the late 1950s and 1960s. The Tape Recorder (November 1960) noted that Ampex lavished the same specialized test gear on its professional Model 351 as on £5,000 computer recorders running eight tracks at 150 inches per second — a factory-floor detail that says something about how the company positioned the 351 in its professional line. It wasn't a toy, and it wasn't treated like one on the test bench.
Collectors should go in with eyes open. These are tube machines, which means capacitors, and tubes, and the slow attrition that hits any sixty-year-old amplifier. The consoles are heavy and awkward to move. The full-track format limits practical use to mono playback and archival transfer work, and tape stock for quarter-inch mono is a smaller pond than it once was. But the electronics are the draw, and the fact that a modern plug-in developer chose these specific circuits as the target of a commercial product is the strongest argument for the 351's continued relevance. It's not a museum piece because it looks old. It's a museum piece because people are still trying to sound like it.
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