Revox A77

Revox A77 – the insider tip of many insiders – restored, modified, made old again .

What a story this machine had!
Dusty, taste of nicotin, technically defective, it was pushed to me by a friend, which I had previously revised a Revox B77.
His wife once again wiped dust and said: “…… you can not push anyone in the hand!”

Revox is generally considered to be repairable because of the passable replacement parts, and this – forgive me the term – almost scraped model should all previous restoration experience are used.
And to say it in advance: it was worth it !!

More with pictures than with text I try the restoration and the conversion of a 4 track machine to play 2 track machine.

As always the initial situation :

– Revox A77 9.5 / 19cm speed

– 4 track machine

– No activation possible

– All exterior parts of a rich nicotine tar coating provided

– no big obvious defects

Tool used :

– Ultrasonic cleaner

– Various screwdrivers and spring ring pliers

– Dishwasher my wife

– Multimeter, oscilloscope, soldering station

– Camera for documentation and restoration

– Service manual of the company Revox (Downloadversion

Disassembling the machine:

Here it means – actually as always – to proceed cautiously and in particular with the plastic control units to exercise care.

Aggressive chemistry, a prolonged use of the US cleaning machine and something is irreparably defective.
First of all, I have removed all removable keypads of the Revox A77.
Left picture: you can see the uncleaned volume regulator, right the cleaned (controlled US bath under view).
Right picture : the bent front panel, rusted outlet bearing, dusty tape guide.





Some impressions of the disassembly, including the wonderful modular design with the plug-in cards.


Here I had to resort to some tricks and apply all sorts of technology to get back “shine in the hut”.

After express permission of the house management I was allowed to use my wife’s dishwasher to clean the completely gutted die-cast housing. At 40 degrees and only clear water with very little cleaning additive everything shone in new splendor



All pictured parts have survived the machine well, the drying was of course shut down in the cleaning program.

Purely mechanical parts and the board after unsoldering the moving parts were cleaned in the ultrasonic bath with standard cleaner, as well as metal parts (hangers, bearings, ….). Important: Then rinse thoroughly with Aquadest and air dry !!

Restoration Revox A77:

1. Engines:



The two winding motors were provided with new, closed bearings, the associated circlips were also exchanged. Amazing that when only motors mounted rotating the bell made a silent run, where previously dtl. Stock sounds were heard.

Left picture: … the disassembled motor with corroded bearing Right picture: New installation of the right winding motor

2. Capstanmotor:


Here, too, I changed the bearings and gently removed the drive shaft from corrosion. The rear mounting on the die-cast chassis is completely trouble-free

3. head carrier:

Since all machines run in two-lane mode with me, a change was announced here (and in electronics). ebay gave me in Italy a complete head support with 2mm (!!) mirror for 35 €. A stroke of luck.

After thorough cleaning and demagnetization, he found his new place in the age-old machine.


Again, the right and left inlet / outlet storage had to be changed. In view of the excellent quality and availability of German ball bearings no problem. There is nothing to scream or loll about when fast-winding.

In the same way, the main drive motor and the left winding drive were repaired.



Left picture: … the rebuilt engines Right picture: cleaned pull magnet and new protection diode



Left picture:. ..the new 2 track headset Right picture: the drive buttons after US cleaning

4. Brakes and residual mechanics


… .so slowly the machine rebuilds …… ..



Provisional construction and preliminary test of the mechanics -> that works!
The brakes, solenoids, belt mechanics are set according to service manual. Helpful here is a Correx spring balance, with which the trains can be set well.

5. Power supply and electronics
Now it’s time for the electronics.



Left picture:. ..the reconditioned power supply board Right picture: the connection field after cleaning



In the revision, I proceeded – well justified – gently .
From the exchange of semiconductors against low-noise types I have apart and defective tried to replace with original types .
Had to believe:

– Trimmer (good Piha’s)
– Elkos’s (Panasonic vs Frako)
– Motor capacitors
– defective potentiometer of the volume control
– Illuminants


Thanks to the modular design and the excellent documentation, the “rebuilding” process succeeds without problems.
All electrical contacts were carefully cleaned mechanically and treated with special contact spray, fats and / or oils were not used.



During commissioning, a potentiometer went on strike on the “mainboard”, namely the volume control.
Here is my special thanks to “the DIN standard” and the old design.
Such a pot is still verschaubt and thus dismantled !!!!!!
And from modern productions coal railways and grinders can be taken over for partial revision. That should hardly exist anymore !!!

6. Final construction and calibration

Finally, the machine was measured according to service manual and the instructions of Mr. Bluthard (3 volumes on the subject) and enjoys the best of health!

And old last gimmick I swapped the mechanical counter for an electronic one.
This works great and is green well readable from a distance.

7. sound

The sound: difficult to describe but

warm and musical
– fits very harmoniously into the existing tube chain
– great musical rendering of tapes mastered on my Studer A810
– altogether more pleasant than the likewise revised Revox B77


8. Conclusion

This “scrap-ready” original machine is practically new and has excellent readings at 9.5 and especially 19.5 cm / s in two-lane operation. My greatest respect to the developers who “invented” this fine machine.

Dortmund, 19.7.2016

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