CONNECTIONS FOR 120-VOLT OUTPUT
(MT125A ONLY)
Figure 3 shows connections for 120-volt output at
selected frequencies for laboratory or industrial
applications.
POWER CONNECTIONS.
The booster amplifier may be operated from 120 vac or
48V to 56V dc.
120 VAC SOURCE. Connect the ac power cord to a 120
vac. source. Use a 3-wire receptacle with the center pin
connected to earth ground.
If desired, auxiliary equipment may be connected to the
AUX POWER receptacle on top of the unit. Do not exceed
power ratings on the schematic diagram.
48V - 56V DC SOURCE. Connect the amplifier to a dc
source capable of delivering power indicated in the Techni-
cal Specifications table. A two-prong polarized plug (Bogen
Part No. 85-0109-01; Cinch Jones No. P-302-CCT) is
supplied with the amplifier for making dc connections.
Connect dc cable to source making certain to observe
proper polarity.
VOLUME CONTROL
A volume control located on the rear of the unit is used
primarily to compensate for variations in preamplifier
output levels. The VOLUME control permits the gain of the
amplifier to be preset so that the preamplifier volume
control may be operated near the center of its range, rather
than at an extreme maximum or minimum. The VOLUME
control is a screwdriver adjustment which needs to be set
only once for any given preamplifier input.
DC POWER OPERATION
When the amplifier is operated from a dc power source,
the ac power switch and ac power indicator lamp will be
inoperative and there will be no power at the AUX POWER
receptacle on top of the chassis. Turn the amplifier on and
off from the power switch on the dc power supply or by
inserting and removing the dc power leads on the rear of
the unit.
M A I N T E N A N C E
AC OPERATION
There are two overload protective devices used with ac
operation, the circuit breaker and the temperature overload
thermal breaker.
AC CIRCUIT BREAKER. If the circuit breaker opens, the
ac power lamp will go out and the amplifier will have no
output, but there will be power at the AUX POWER
receptacle on top of the unit. Set the ac power switch to
off and momentarily depress the red button on the circuit
breaker to reset it. Return the ac power switch to on. If the
breaker trips again, do not attempt to reset it but have the
trouble investigated by a qualified technician.
THERMAL BREAKER. If the temperature thermal breaker
opens, there will be no audio output but the ac
power lamp will remain on. Wait approximately two
minutes for the breaker to reset. If the breaker resets and
then opens again, investigate the cause of the temperature
overload. This may be due to improper connections at the
output terminals or to excessive environmental heat with
inadequate ventillation. The thermal breaker will open
when the temperature at any one of the output transistors
is excessive.
DC OPERATION
There are two overload protective devices used with dc
operation, the circuit breaker and the temperature overload
thermal breaker. If either device opens, there will be no
audio output. The ac power lamp does not light during dc
operation.
THERMAL BREAKER, See the applicable paragraph under
“AC OPERATION”.
REPLACING TRANSISTORS
Transistors show little, if any, deterioration with age and
are considerably more reliable than the best vacuum tubes.
This is why some transistors are soldered into equipment
like resistors or capacitors. If the unit is inoperative, it
generally is safe to assume that the transistors have not
failed and that the trouble is elsewhere in the equipment.
If a transistor must be unsoldered for testing or
replacement, be certain to remove all power from the unit
to prevent possible voltage transients in the circuit which
might damage the transistor. To prevent overheating the
transistor when soldering or unsoldering a lead, grip the
lead between the point of heat and the case with pliers or
tweezers. These will act as a heat sink to conduct heat away
from the transistor. Do not bend a transistor lead closer
than 1/ 16” from the transistor case.
Power transistors must be properly mounted to insure
good heat dissipation. Make certain there is no foreign
matter on the contact surfaces between the transistor and
the heat sink and brush a thin coating of heat transfer
compound (such as Dow Corning No. 340 Compound
silicon grease or equivalent) on both surfaces. Similarly coat
any insulators used between the transistor and the heat sink
and secure the transistor firmly to the heat sink.
BOGEN SERVICE
We are interested in your Bogen equipment for as long as
you have it. If trouble ever develops, do not hesitate to ask
our advice or assistance. Information can be obtained by
writing to Service Department, Bogen Division, P.O. B
O X
500, Paramus, N.J. 07652.
When communicating with us, give the model and series
designation of your unit. Describe the difficulty and
include details on the electrical connections to and the
types of associated equipment, such as preamplifier,
speakers, etc. We will send you service information if the
trouble appears simple. If the trouble requires servicing, we
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