Revox A77 Service Manual

Power supply board 1.077.540 carries the output amplifier
connectors.
The electronically regulated voltage ( 21 V) for amplifiers
(and oscillator) is adjusted at P 106. The transistor Q 102
acts as a series regulator, whose conductivity is controlled
by Q 101. The zenerdiode D 104 provides a 12 V reference
for the emitter of this latter transistor.
Diode D 103 protects the base- emitter diode of transistor
Q 101 from overload in case of possible short circuit in the
amplifier section.
5.9. Drive Control
( 1.077.370, Diagram Tape Drive 1.077.100)
I Removal per 3.8. I
Fig. 5.9-42
The drive push buttons operate contacts on control board
1.077.370. Remote control contacts can be paralleled to
these contacts ( remote control contacts F3 to F10 ). To
have a minimum of relays, their control is locked by diodes.
The principle of their control is explained by an example
for better understanding. In the circuit of fig. 5.9 — 43,
relay A is energized and contact a 8/12 I self- holding I
is closed. This corresponds to mode PLAY. Relay B is
without current, contact b 6/10 is open.
R119
Fig. 5.9-45
+ 27 V
R111 1R113
4
12
+ 27 V I
12
A
8
STOP
6
10
PHOTO- ELECTRICAL
END- OF- TAPE SWITCH
Fig. 5.9-43
If button << is depressed, relay A is shorted and drops off.
Simultaneously relay B is energized and holds itself over
self- holding contact b 6/10. Self- holding can be interrupted
by the STOP button or by the photoelectric end- of- tape
switch. The following table indicates which relays and sole-
noids are energized for corresponding functions.
Table 5.9-44
A B C Record
Relay
Roller
Solenoid
Brake
Solenoid
STOP
PLAY x x x
>> x x
<< x x
R EC
x x x
x x
To avoid loose tape loops at record and playback starts,
the right-hand reel motor receives elevated voltage for
about 0.3 sec ( winding reversal voltage 105 V ). Relay C
must be energized a short period for this, accomplished by
the following circuit :
ROLLER
SOLENOID
BRAKE
SOLENOID
v 2 10
011111«la
a
11
8
3
7
a
REL.A
D121
REL.0
III
CV
D120 C111
11
D123
I
Il
L

Revox A77 Specifications

General

Brand	Revox
Model	A77
Category	Tape Deck
Language	English