The Revox A77 is the one tape machine in this archive with real serial brackets — and it needs two of them, because the A77 was built in two places at once.
Two parallel streams
A prefix letter selects the place of assembly, and each stream has its own scale:
- S — Swiss build. S 054–S 18,080 covers 1967–1969; the last documented Swiss range runs from S 72,853 onward, 1973–1977.
- G — German build. G 100–G 19,368 covers the same 1967–1969 window; G 145,100–G 289,836 covers 1974–1977.
The prefix is the place of assembly, not a version. That misreading is common enough that the archive prints the correction beside the result.
Versions: Mk I to Mk IV
The version marker is a separate system. A restoration guide in the archive's sources dates Mk I to 1967–69, Mk II to 1969–71, Mk III to 1971–73 and Mk IV to 1973–77, which agrees with the period service manual to the year. A version bound plus a prefix-selected range is what the archive reports: not a build date, but a defensible window — and the window is what a buyer or a restorer actually needs.
Where the exact date survives
On the A77, month and year are stamped on the motor rotors. That is the closest thing to a build date on the machine, and the one place where an exact month can be read. It also requires dismantling the unit to reach the motors, and the archived guide is written for technicians rather than for a beginner — so the archive reports the version bracket from the serial and points to the rotor stamp as the next step, rather than telling you to take the deck apart.
The rest of the Revox range
The B77 is bracketed in two halves: 1–100,000 is 1977–1980 and 100,001–220,000 is 1980–1989, about 220,000 units in total. Beyond that the archive is honest: the PR99, A700, G36, A80, A810, B215 and B710 are undated here, because no reachable source dates them. The G36 has internal modification points recorded (serials 36,500 and 58,000), but a modification bracket is not a build year and is not presented as one.
See the Revox archive for the full series list, the rotor-stamp guide and the decoder.