For those that don’t know, Studer is the parent company of Revox. The Revox brand was marketed as high end consumer stereo equipment, the Studer brand more for pro audio and studio use.

Tube Revox decks– the D,  F and G series were some of the original tube reel to reels offered to the high end stereo market in the 1950s and 1960s.  There are many of these decks available on the used market, with many still working, however they have their own unique set of problems.

While the electronics of the decks are generally in great working shape, and they don’t seem to have the capacitor problems of the later A and B series of decks, the electrolytic capacitors should still be changed out due to age. We do this on every tube  Revox we get in here.

The fine point to point wiring in a Revox G36

There are no other typical problems with these older tube decks, although brittle plastic is pretty common, especially for pieces like the tape counter. There’s not a lot of spare parts available for these decks, and finding a good working tape counter is very difficult at this time.

Beware that there were several revisions within each of the models, and things like the speed selector switch varied between models, and they are not interchangeable. Also, the heads in the F and G series are somewhat softer than in later models, so with a deck that was used regularly, the heads may be in bad shape. Replacements are generally hard to find.

Given the age of the F and G series of Revox decks, we recommend that while they make a great collector piece, we don’t recommend that you use one as your daily driver model. Instead, use it sparingly, and rely on a later machine for regular use.

A77, A700- the Revox A77 came out in 1967, and was in production until 1977. There were 4 different models of A77s, the MkI to the MKIV. While a number of boards can be interchanged between the various versions, each new model had different refinements.

Bad Capacitors- Revox is well known for their exploding Rifa motor capacitors, that can fail at any time, filling you room with smoke, that will linger for hours. The A77s used 4 of these capacitors, that we change before even powering a deck up. It’s a mandatory replacement on any Revox deck.
The A77 also used Frako brand capacitors, that are known to leak and to short  out at random. Again, each A77 needs a mandatory full recap if it’s going to be reliable, and perform to spec.

Bad trimpots. Revox used large adjustable trimpots in each deck, about 16 in total on each A77. These large trimpots go brittle over time, and the adjustment arm that sets the value can snap off without warning, resulting in any number of audio or speed problems.  Failure is so rampant at this point that all trimpots get changed in any A77 that comes through the shop.

Bad bearings- not too difficult to change, but most A77s that have been stored for decades, particularly in a damp basement, has rusty bearings that have resulted in seized motors, or very noisy FF or REW. We change them as required.

Revox A77 showing the modular construction. Each board is full of bad caps.

Bad VU meters- the glue bonds within the VU meter movements tends to become brittle and break, resulting in a stuck meter. The demand for used meters has skyrocketed in recent years, to the point where a used 50 year old VU meter runs $50-75 US each on eBay. The other alternative is to purchase new meters, however they are even more expensive, and need to be changed in pairs, as they look different than the originals. Note that the black faced VU meters of the MkI and MkII cannot be interchanged with the silver faced ones of the MkIII and IV.

Overall, each Revox A77 needs $500-800 USD worth of work done to it to make it reliable. New capacitors and new trimpots are mandatory, and most decks need additional service work done beyond this work as well.  Without  the recap and all new trimpots, it’s not worth working on  an A77 model at this time.

The A700 came out in 1973, and had many unique parts to it, and is considered to be a problematic, overly complicated unit. It shares all of the same problems with the A77, which is why we’re putting it in the same grouping.

B77- The B77 replaced the A77 in 1977, and the somewhat similar PR99 came out in 1980. While many of  the PR99 circuits are different and not interchangeable with the B77, the basic operation is the same, as is the typical age, so we’re lumping them together.

Bad Capacitors- as with the A77, all B77s and PR99s need the Rifa motor capacitors replaced, and at very minimum, all Frako capacitors and main filter capacitors should be changed as well. Ideally,  an entire recap should be done, however the smaller capacitors on the various PC boards don’t fail as much as in the older A77s, so for a budget repair/service, those can be left as-is.

Revox B77

Trimpots- the same large trimpots in the B77 and PR99 fail in these models as the A77, however the PR99 switched to some smaller version trimpots that are far more reliable than the large ones. Changing the large trimpots is mandatory, changing the small ones is optional.

The bearings, VU meters, and other components listed in the A77 writeup can also fail in the B77 and PR99, however since these are later models by as much as 10-15 years, failure isn’t as much as in the older models.

Studers- The Studer line was the pro division of Revox, and Studer made many killer decks for radio and TV stations, and recording studios alike. Studers are overbuilt, and quite a bit more complex in  general than the consumer decks, so there’s more to go wrong with them as a result. All of the problem areas that affect the Revox line also applies to the Studers, and I’ve found shorted capacitors in late model (1990) Studer machines. A full recapping is mandatory, along with a proper alignment.

Multitrack decks, up to 24 tracks have failing capacitors. A typical 24 channel deck needs 475 capacitors replaced (that was the count on the one A80 24 track I rebuild 2 years ago), so repairs aren’t cheap, but neither are 24 track decks.A typical rebuild labor time for a 24 track deck is in excess of 100 hours.

Many of the trimpots were eliminated in Studer machines thanks to microprocessors, which use digital pushbutton adjustments to set the value. These microprocessors use a memory battery that is generally rated to be good for 5 years, however most will last in excess of 10, or even 20 years. HOWEVER.. these batteries tend to leak, causing eventual damage to the PC board traces. Leave it long enough, and the board will need to be replaced due to too much corrosion damage. Battery replacement.. complete with  a sticker indicating the month and date is mandatory on all Studers that use MPU board batteries.

The stunning Studer A820, without reel tables attached.

Rollers/bearings. Most Studers were put to use for many hours, resulting in worn bearings or rollers. Replace as required.

VU meters can also fail in Studers. I haven’t found any generic replacements, so I’ve purchased used preamps or meters on eBay as required.