greening the - Audiovintage

1|-r|* audio hobby has, I believe, a de\-/voted group who collect and en-
joy listening to prerecorded tapes. This
article addresses what I believe to be an
v'
GREENING THE }
REVOX G36
ided tub€d playback machine for those
tapes, the Revox G36.
Literally hundreds of types of open_
reel descendants of the German Magnetophone were produced from the late
1940s to the present day. The prerecorded open reel (PROR) tape medium
staned in the early fifties, in mono, of
By Charles KIng
course; stefeo was introduced a few
years later. The origind stereo format
was half-track, but as tape head technol_
became
ogy improved, quarter-rack
cofllmon in the late fifties.
The advent of the eight-track cassette
and the eventual dominance of the Norelco format, eighth-inch cassette, with
its ease of use and reduced storage requirements, sounded the death knell for
the PROR medium by the early seven_
ties. I believe only one outfit is crurently selling PROR format tapes and their
catalog contains perhaps 5O choices.
As indicated, nxrny open-reel machines were produced which can be
used for listening and ofcourse, record_
.
-
ing. Due to my preference for tube
equipment, the available field is narrowed substantially, to machines pro_
, duced by Ampex, Crown and Magnecord, along with the Revox G36. -The
Ampex and Crown products were pro_
fessiond machines with excellent sonics.
However, a unit ingood condition now
fetches upward of $1,O00. Spare parts
are available, but are very expensive,
and the transport mechanism and elec_
tronics are separate, making the units
large, requiring Sherpas for moving.
My limited experience indicates ihat
spare pafts for the Magnecord units are
all but impossible to find.
The Revox products are very high
quality, and most imponantly, mechan_
ical and electrical parts for the G36 are
still available and reasonably priced.
Revox G36
Revox' original 36;;;;""rd.*
1us.
ing an "A" prefix) premiered in 1954,
using three motors with no belts or fric_
ArcUT
AI]IHON
Cturles King is a confirmed adio
.'-;
modifer
and
urcbmphile, having experimented with mrny desigs
which have appeared in TAA LrfrJe,. ttis orreirt systim
]il
"8"
version
evolution reached its zenith with the
G36,
in
production from tg64-67,
which was then superseded by its transistorized counterpaft, the A77. In all,
over 80,0OO J6-series machines were
produced.
If I interpret the service manual correctly, the "G" series started with serial
number 35001. The frst version incor-
porated a lever switch to sense the
presense of moving tape, and had no
bias trap in the reproduction circuitry.
The second version (around 4g4}l)kgan using the bias trap, lrevised motor
control circuit, and a minor change in
the record ampli_fier to limit the high-
frequency response. The "Mark 3"
series (around 58000) inctuded an
op
tical tape sensing mechanism, and
a
redesigned capstan motor/capstan coupling assembly to further reduce fluner.
During the Mark 3 production run, a
new lower voltage bias oscillator/erase
head was fitted-on two-track (from
69701) and four-track machines
(60 101-60700 and
6l l0l-6s50o).
I believe only cenainproduction runs
in the Mark 3 series were specifically
designed to use 6OHz and exported to
the US. The 50Hz European machines
can easily be adapted; more on this later.
Also, cenain Mark 3 units were designed
for high speed use, 7lL-15 ips.
Chccking a G36
THE
dso trCndes a mrrh nodtEed Braln
recorda.
tion wheels. In 1956, the
appeared with rparate record/playback
heads. The first stereo version, the D36,
was introduced in 196O. The machine's
IGl000 r€eLtord
Grlss AUDro o/sa
My knowledge extends to the two G36
machines I currently own and four other
units I've worked on over the last few
years. Prices vary, depending on the
unit's condition and the seller's awate-
I pzid $7 S for one unit
$275 for the other, and I haye seen
a high-speed, half-track unit advertised
for $500.
Check-out is relatively simple: Utilizing a cheap tape, ensrrre that all the
mechanical functions appear to work
propedy. Then clean and demagnetize
the heads and play a reference tape.
Leave the unit on for a while and listen
for any squealing noise from the capstan
motor, which may indicate a bearing
problem. Check the tape heads and cap
stan shaft for wear, which will give an
indication of how much the machine has
been used. Look for stripped tape head
adiustment screws to see whether the
unit was ever worked on, and pull off
the grey knobs to see wtrcther the white,
felt washers are still in place, which keep
the knobs from scratching the clear
plastic switch collar.
A seryice manual for the G36 is available from StuderlRevox, l4Tj Elm Hill
ness of its value.
aurrd
\
_/
Pike, Nashville, TN 37210, (6rj) 2j45651 . The following discussion refers to
sections and part descriptions from the
manual (see schematic).
Tape Heads
The origind record and playback heads
were unshielded and instalted in small
cylindrical cans. A slot in the can allowed for tape contact, and the coffEcting wires emerged from the open bottom of the can. Sometime later, new and
improved interchangeable heads were
made availehle for the mzcl'ine. Tablc
I lists what I believe are the current part
numhrs for the various heads.
The new heads are shielded, eliminating the need for the cylindrical can,
and have rear solder connections. An
old head may be removed by unscrew-
)