Revox A77 Service Manual

— Set minimum voltage at BIAS TRAP CH 1 and CH 2:
Less than < 300 mV ( fig. 6.4 — 64 ).
o MR\ LEVE1
MOOR, MOTO OSCREATOR
CIII Cm I
0 t 0
EOM. . 1
0 0
C T:. 0 »% 0
c.. 10.T . el
OSPROCIVCE
• 0. 1.1
•
Playback Record
Fig. 6.4-64
/MEOW MIIILIF
11 :" 0
RECORD & TIRO
0
EOM.
-0
0
RITTER 0
CALIF
TR "" /1/1 11111111
6.4.4. RF - Traps, Playback
— Under same conditions as 6.4.3. but, connect VTVM to
OUTPUT terminals CH 1 and CH 2 and set BIAS TRAP
of playback amplifier to a voltage minimum : Less than
< 50 mV I fig. 6.4 — 64 I.
6.5. Record - Adjustments
Preparations :
Following measurements ( 6.5.1. to 6.5.6. ) are to be taken
with a record level of — 20 dB below full modulation level.
( To avoid over- modulating high frequencies ).
— Set controls per fig. 6.5 — 65.
MONITOR
MAX
Fig. 6.5-65
[MANN I
'WORD
— Connect AF-millivoltmeter to OUTPUT terminal.
— 300 mV range
— Adjust AF- generator ( 3 - 4 mV ) at 1000 Hz to obtain
200 mV at the OUTPUT terminal ( voltage as for play-
back from test tape per 6.3.3, but 20 dB lower ).
6.5.1. Azimuth Adjustment, Record Head, Coarse
— Set controls per fig. 6.5 — 66.
MONITOR RECORD
MAX
Fig. 6.5-66
MAX
Fig. 6.5-67
0
— Set AF- generator to 10 kHz ( see 6.5. preparations ).
— Load tape and switch to RECORD.
— Adjust for maximum signal with screw B ( fig. 6.5 — 67 ),
( turn slowly — indication delay ! ).
6.5.2. RF - Bias
Since the high frequency playback voltage is bias dependent
in a curve with distinct maximum, a relationship which can
be used to determine the operating point ( fig. 6.5 — 69 ).
The measurement is per 6.5.1. I 10 kHz, — 20 dB 1.
Controls OSCILLATOR CH 1 and CH 2, 3.75 and 7.5
( fig 6.5 — 68 ) are turned from the left limit in clockwise
fashion until maximum AF output voltage is reached ( play-
back mode switch by choice CH 1 / CH 2 ).
0
REIIR LEVEL
C1.1 REIROMMI RION.INTII . 3
M.• TRIO
Fig. 6.5-68
0
o
MOON, « MR 0.11.1•1011
C.
3% le
!MR. CM I
1111
0
- 0
CIM
•
IRCORD
0
MCONJ MORO
CM I
»% 0
EDUALEL
-0
RIM 0
Note the pointer deflection at the maximum and continue
turning in the same sense till AF- output voltage has dropped
by the amount ( AV ) shown in the following table.
V(AF)
10 kHz
max
Operating Point
Bias
Fig. 6.5-69
29

Revox A77 Specifications

General

Wow and Flutter	0.08% (7 1⁄2 ips)
Frequency Response	30Hz to 20kHz (7 1⁄2 ips)
Signal to Noise Ratio	60dB
Type	Reel-to-Reel Tape Deck
Track System	4-track, 2-channel stereo/monaural
Reel Size	Up to 10.5 inch reel
Motor	2 x reel, 1 x capstan
Inputs	Mic, Line
Outputs	Line
Tape Speed	3 3⁄4 and 7 1⁄2 ips