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Revox built the A77 from 1967 and the B77 from 1977. Between them they are probably the most widely owned serious reel to reel tape recorders ever made, and they are still being restored today, in numbers, by people who were not born when the last one left the factory.
They survive for a straightforward reason. Studer designed them to be serviced. The electronics sit on plug-in boards, the mechanism comes apart in a defined order, the factory documentation is thorough, and almost nothing inside is a sealed module. A machine that has been stored badly for thirty years is a weekend of work, not a write-off.
This is the index to five guides. Each one is complete on its own. Together they cover buying a machine, bringing the mechanism back, bringing the electronics back, setting speed and alignment, and looking up any part number you meet along the way.
Where to start
It depends on what is in front of you.
- You are looking at a machine you might buy: start with the buying guide.
- The machine will not power up, or powered up and did something alarming: start with the electronics guide.
- It powers up but will not move tape properly: start with the tape transport guide.
- It runs but the speed or the sound is wrong: start with the speed and calibration guide.
- You know what the part is and need its number: go straight to the parts reference.
If you have a machine that has been in storage for decades and you have not powered it up yet, do not power it up yet. Read the section on mains film capacitors in the electronics guide first. Those parts fail destructively, and the failure usually happens on the first power-up after a long rest.
The five guides
Buying a Revox A77 or B77
Both models ran for many years with running changes, so two machines with the same badge can differ in head block, track format, speed pair and electronics. This covers which versions exist and how to tell them apart, what the Revodur head material means for a machine that has already run for decades, what the rear panel sockets are actually for, and which faults are routine against which faults should make you walk away.
Tape transport restoration
The mechanism as one system. Overhauling the transport, freeing and adjusting the brakes, replacing the tape counter belt and its gear with standard stock parts rather than expensive service items, and fitting a new pinch roller. These are the jobs that stand between a machine that sits on a shelf and a machine that records.
Electronics: boards, capacitors and power faults
How the plug-in boards are arranged and what each one does, what to check when the machine will not power up, why the mains-side film capacitors fail the way they do, and how to work through the capacitors on the drive and audio boards. Electrolytics age whether the machine ran or not, which is why a deck that was put away working will not be working now.
Speed and calibration
How the capstan motor holds speed, what the speed control board does and how to set it, calibration of the high speed capstan board, and how to set a tape speed the machine was never built for. This is the work that comes after the mechanism is sound, because measurements taken on a poor transport describe the transport rather than the circuit.
Parts reference, searchable
Three tables with a search box on each: an English and German glossary of every part in the tape path, the full exploded view across five assemblies, and every capacitor position across six circuit boards. Type a part number, a part name or a board name and the table narrows as you type.
On the documentation itself
Much of what is here comes from the factory service manuals, checked against machines that have actually been through the work. Where the two disagreed, what the machine did is what is recorded. These recorders were built over many years with changes that never made it into a printed revision, so if the part in your hand does not match the entry in a table, your machine is right.
One habit is worth more than any single procedure. Before you undo anything, photograph it. Not the whole machine, the specific assembly, from the angle you will be looking at when you put it back. Nobody has ever regretted having that photograph.