Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER Instruction Manual - page 20
2.1. POWER SUPPLY
All models of the NAGRA 4.2 may be powered either by an external power supply (ATN-3) or
alternatively by internal batteries. The 4.2 will accept voltages ranging from -11 V to -30 V with
peaks of up to -35 V. The batteries are placed in the bottom of the machine and the polarity is
marked inside the battery compartment. Turning the two fasteners with a screwdriver or a small coin
opens it. All the batteries MUST be orientated in the same direction as indicated on the base of the
battery compartment.
The NAGRA 4.2 houses twelve "D" type 1.5 V cells having a maximum diameter of 33.5 mm and a
length of between 59.5 and 62.5 mm. It is important to remember that corrosive material can leak
out of flat batteries, causing severe damage to the recorder, and therefore it is recommended not to
leave batteries in the machine during periods of storage.
If leakage occurs as a result of leaving flat batteries in the machine, then wash the affected area
with fresh water. The machine will suffer much less from the water than the electrolyte from the
batteries. The external supply is fed into the machine via connector marked POWER PACK (48) on
the right-hand side of the machine. Rechargeable batteries may also be used and can be charged
using the ATN-3C (order no 14376), which includes the charger circuitry.
The 4.2 will function when the power is as low as 12 V (at 15 ips - 38 cm/s) and down to as low as
10.5 V at the lower speeds. (These figures correspond to a machine in perfect condition and
working at room temperature).
When using an external supply, selector switch (3) must be in the "EXTERNAL" position. It must be
in the "BATTERIES" position when internal batteries are in use. It is not necessary to remove the
batteries when working with an external supply (and vice versa).
DANGER OF REVERSED POLARIZATION
A reversed polarized power supply (negative to the chassis) WILL damage the machine. To reduce
the risk of serious damage a diode is placed in parallel with the supply, which will be short-circuited
in the event of, reversed polarization. If such an event occurs with normal "dry cells", they will be
rapidly exhausted and no further damage will occur.
On the other hand, certain accumulators are capable of supplying sufficient current (in excess of 8
amperes) such that the internal wiring of the machine will become hot enough to cause its insulation
to decompose. This will then liberate gas, which causes considerable corrosion. If this happens,
contact your nearest NAGRA agent immediately.
MEASURING BATTERY CONDITION AND POWER SUPPLY VOLTAGE
BATTERY RESERVE
When the Meter Switch is put into the "Batt. Reserve" position the meter will indicate the difference
between the power voltage available and the power, which the Nagra needs. Often the two voltages
will fluctuate. The device will take into consideration the lowest instantaneous voltage and
memorize this. This detail is important, for the average voltage of a power supply can be sufficient
but momentary drops in the voltage can happen and drop lower than the required minimum.
New batteries will give about 18 V whereas the Nagra can be powered by up to 30 V. This explains
why, with new batteries, the needle of the meter will only indicate about 40% full scale, when it is
switched to "Batt. Reserve".