Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER Instruction Manual - page 21
VOLT / CELL
The meter switch in this position works as a simple voltmeter. The centre scale is graduated from 0
to 1.6 V, it indicates 1/12 of the total voltage or the average voltage of 1 cell.
The position Volt/Cell is essentially designed to monitor the voltage of some accumulators, which
would be damaged if they were allowed to discharge below a certain value. This value is 1 V /Cell
for certain manganese dioxide alkaline accumulators.
It is also possible to monitor the external power supply voltage. If when in the position "Batt.
Reserve" position the indication is that the Nagra is not receiving sufficient voltage, but the Volt/Cell
indicates that the power supply voltage is correct, this means that the Nagra requires an abnormally
high voltage. Under these conditions the motor and motor collector should be examined.
MEASURING THE MOTOR CURRENT
The meter will measure the motor current when the meter switch is in the position "Mot". There is no
corresponding scale on the meter but the "Volt/Cell" scale can be used.
Full scale deflection corresponds to a motor current of approximately 250 mA. In "no load" running,
i.e. without tape and with the pinch wheel separated from the capstan (but not in the rewind mode),
the needle should indicate between 0.2 and 0.3 V. If this value is exceeded, see paragraph 6.2.
"SPEED & POWER" INDICATOR
At the lower right-hand side of the front panel there is a rotary indicator marked "SPEED &
POWER". Under normal circumstances a white cross should appear, but it will disappear when:
a.) the power supply voltage becomes insufficient.
b.) the motor current reaches its maximum value. In this case, the speed
stabilizer requires the motor to go faster, but this is not possible as the
current limiter has already reacted. Thus there is a strong probability that the
speed will not be correct.
c.) tachometric WOW is out of tolerance.
In summary, if a white cross appears on the indicator the operator may be sure that the power
supply is sufficient, that the motor turns at the correct speed, and that the tape speed is correct.
EXTERNAL POWER SUPPLY
On the right-hand side of the machine there is a 6 pin Tuchel-type T 3403 connector marked
"POWER PACK". The corresponding plug is the T 3400/1.
The connections are as follows:
pin 1
Battery negative
pin 2
Chassis (positive)
pin 3
Pilot playback output
pin 4
Speed correction signal input
pin 5
Negative external supply
pin 6
-10 V stabilized output.