The Revox A77 MK1 was
introduced in 1967. It was the first fully transistorised 3 motor 1/4inch tape machine from
Revox utilising Studer Heads, Motors and other parts.
CLICK HERE to view the A77 MKII description
CLICK HERE to view the A77 MKIII description
CLICK HERE to view the A77 MKIV description
First available with a wooden or an alloy chassis mount sleeve the unit was available
with 2 speeds - 71/2 and 33/4
Second being controlled by the rotary
Mains On/Off Switch on the right hand side of control panel. Much thought had been put into this machine - it even offered
different reel tensions dependent to the spool size in use controlled by the same Mains Switch!!!
Later in the build Revox used a larger capstain shaft in the Studer Capstain Motor which allowed
the unit to run at 15 and 71/2IPS.
This "Studio Quality" style machine gave a better signal to noise ratio at the higher speed
and allowed the unit to be bought and used in many recording studios around the world.
As the silver finish control panel had been silk screened in bulk, Revox issued the fast speed
machine with little stickers marked 15
over the 71/2
silk screen motifs on the panel respectively.
European models had a different set of High Speed stickers marked
relative to the 15
These European speed qualification stickers measure the
tape speed in Centi
Metres per second.
The High Speed A77 had a couple of minor modifications to the motor internal control board from that of the lower speed unit.
Although the boards look similar - trying to make the units operate at the correct speed is sometimes difficult to calibrate
with an incompatible board installed.
Later recommended modifications to the Relay Board - giving a greater tension to the
tape rewind for 7" spools - by replacing the large 900 ohm wire-wound resistor (R125) with a 9 Watt 1.2kOhm equivalent became
a standard item to check when servicing.
The Revox A77 MK1 looks similar to the later MKII - all panels, cases, parts etc being the same -
except for the tape path transport on the MK1
which offered a fixed left hand post guide as show in the graphic on the right. This - externally - is the only way you will be able to
identify a MK1 unit - which would date it from 1967 to late '69.
The A77 MK1 was available with 2 tape formats - the 1/2 track (2 track) and the 1/4 track stereo (4 track).
Please CLICK HERE to refer to the `Tape and Track Formats` page for a more in-depth description of track use.