Revox B77 / A77 Tape Recorder Parts Reference: Exploded Views, Capacitors, Terminology

When you restore a Revox B77 or A77, the soldering is rarely the hard part. The hard part is finding out what a component is called, what number Revox assigned it, and what you can reasonably put in its place four decades later.

This page gathers three lists into one reference. Each has its own search box: type a part number, a part name or a board name, and the table narrows as you type. Nothing is hidden from a search engine or from you. Every row is present in the page; the box only filters what is displayed.

How to search

Type into the box above any table. Terms separated by a space are combined, so capstan motor returns only rows containing both words. The search covers every column, which means you can look up a part by its order number, by its English or German name, or by the board it sits on. A counter under the box shows how many rows currently match.

Reading Revox part numbers

Across these lists the numbers fall into consistent groups. Recognising the group tells you immediately what kind of item you are looking at.

• 1.177.xxx.xx assemblies and mechanical parts specific to the B77. The 1.177 prefix identifies the model family.
• 1.011.xxx.xx and 1.020.xxx.xx sub-assemblies used across more than one model, such as the push button unit and the tape head assembly.
• 21.xx.xxxx and 23.xx.xxxx hardware: screws, washers, circlips, spacers.
• 50.xx.xxxx integrated circuits.
• 57.xx.xxxx resistors.
• 59.xx.xxxx capacitors.

Values are written in the European style

The multiplier letter stands where the decimal point would be, and a comma is used as the decimal separator. Once you know this, the lists read without ambiguity.

• 2m2 is 2.2 uF
• 4u7 is 4.7 uF
• 10u is 10 uF
• 6800 P is 6800 pF
• 1,2 k on a resistor is 1.2 kilohms

Type abbreviations

• EL aluminium electrolytic
• TA tantalum
• PC film capacitor (polycarbonate)
• C ceramic
• CF carbon film, on resistors
• CER ceramic-bodied power resistor
• RM5 lead spacing of 5 mm, which matters because the boards are tight

Terminology, English and German

Service documentation for these machines exists in both English and German, and the two do not always line up. Searching for a German term in an English forum, or the reverse, is a common way to lose an afternoon. This table gives both names for every part on the tape path and in the audio chain, together with a short note on what the part actually does.

Exploded view parts, by assembly

The B77 mechanism is documented as five assemblies. Below are all 202 line items from those exploded diagrams in a single table, with the assembly named in the first column so you can search across all five at once.

INDEX is the callout number printed on the exploded diagram. QTY is how many the machine uses. ORDER NUMBER is what you quote when sourcing the part.

Capacitors, by board

Every capacitor position on six boards, 270 in total. Pos. is the designation printed on the board silkscreen, so you can find the physical component without a schematic in front of you.

These are the parts that decide whether a machine that has sat for thirty years comes back or does not. The mechanical parts wear; the capacitors simply age, whether the machine ran or not.

Where these parts come from

Mechanical parts and electronic parts are sourced in completely different ways, and confusing the two wastes a lot of time.

For mechanical parts, the Revox order number is the search term. Specialist suppliers who serve these machines hold both old stock and newly manufactured reproductions, and they index their catalogues by the original number. Search the number itself rather than a description. Wear items such as pinch rollers, brake bands, belts and idler tyres are made new today, and a fresh reproduction is usually a better machine than a hardened original.

For electronic parts, the Revox number is almost never used. You read the value and the specification out of the list above and buy a current equivalent from any general component distributor. The number in the list is there so you can confirm you are looking at the right position, not so you can order it.

Choosing a replacement

Electrolytic capacitors

Match the capacitance. Meet or exceed the voltage rating. Check that the diameter and the lead spacing will physically fit, because several of these boards leave very little room. Modern parts rated for 105 degrees Celsius will outlast the originals by a wide margin.

Electrolytics marked FRAKO appear throughout these lists. They have a poor reputation for leaking after several decades, and on most machines they are the first thing worth replacing.

Tantalum capacitors

Positions marked TA can take a tantalum of the same value, or a modern electrolytic at a higher voltage rating. Tantalums tend to fail as a short circuit rather than an open one, which is why some restorers deliberately avoid them in supply positions.

Film capacitors

Film types rarely fail electrically and in most positions can be left alone. The exception is on the mains side, where the safety-rated film capacitors do fail, sometimes dramatically. Those must be replaced with current parts carrying the correct safety class marking, never with a general purpose film capacitor of the same value.

Resistors

Resistors are usually left in place. The ones worth measuring are the high wattage types near a heat source, and carbon film resistors in high impedance positions, which tend to drift upward in value with age.

A note on what this list is not

These numbers come from the factory service documentation for the B77 and A77. They tell you what Revox fitted. They do not tell you which revision your particular machine is, and these recorders were built over many years with running changes. Before you order, compare the part in your hand against the entry in the table. Where the two disagree, your machine is right and the list is describing a different year.