Front Panel Displays And Knobs - McIntosh MC451 Owner's Manual

Front Panel Displays and Knobs

1� METER Control Knob
• LIGHTS OFF- the meter and tube lights will
be off but the dual meter will still respond to
output.
• WATTS - the meter responds to all output.
• HOLD - the dual meter needles will hold the
highest peak until a higher peak is reached.
If no higher peak is reached, the needles will
lower their levels at a rate of approximately
6dB per minute.
Note: When in the WATTS or HOLD position, the meter
and tube lights will be powered On or Off by a
preamplifier or A/V control center connected by a
power control cable if that unit has power control
capabilities.
2� Dual Power Output Meter
Shows both the vacuum tube and solid state
amplifiers' power output. The vacuum tube
scale is displayed on the top and indicated by
the longer needle. The solid state scale is on the
bottom and indicated by the shorter needle.
3� Standby LED
Indicates that the MC451 is connected to AC
power and ready to be turned on via the front
panel knob or rear panel power control.
In the unlikely event of a fault in the MC451's
main power supply, the MC451 will power off
and the standby LED will flash. To reset the
MC451 should this occur, turn the POWER
control knob to OFF, wait one minute, then turn
the POWER control knob to ON. If a fault contin-
ues to occur, the MC451 should be serviced.
6
4� POWER GUARD SGS (Screen Grid Sensor)
®
LED
Indicates when Power Guard SGS is engaged
for the vacuum tube amplifier. Also indicates
vacuum tube warm up.
Power Guard SGS monitors the screen grid
current in the KT88 output vacuum tubes. If the
current becomes too high, a circuit in Power
Guard SGS is activated which then dynamically
attenuates the input signal in real time to keep
the vacuum tubes operating at safe levels.
5� POWER GUARD LED
®
Indicates when Power Guard is engaged for the
solid state amplifier. Also indicates heatsink
over temperature.
Power Guard monitors and adjusts the input
signal in the solid state amplifier section in real
time, then makes unobtrusive adjustments to
prevent distortion and potential speaker damage.
6� POWER Control Knob
• OFF- the MC451 will be powered off
regardless of any power control connection.
• REMOTE- the MC451 can be powered on
and off by a preamplifier or A/V control
center connected by a power control cable.
• ON- the MC451 will be powered on
regardless of any power control connection.
7� Vacuum Tube Input Stage
V1, V2 - 12AT7 McIntosh Part No.165078
V3 - 12AX7A McIntosh Part No.165080
Sentry Monitor™ provides protection by
monitoring current in the output transformer.
In the event of a large impedance mismatch,
a short circuit at the output terminals or tube
failure, Sentry Monitor will activate to prevent
potentially destructive levels of current from
flowing.
When Sentry Monitor is activated, the MC451
will power off, and the three input stage tubes
will flash red.
To reset the Sentry Monitor protection circuitry,
turn the POWER control knob to OFF. Wait one
minute and then turn the POWER control knob
to ON. If Sentry Monitor continues to engage,
the problem must be fixed before continuing.
8� Vacuum Tube Output Stage
V4, V5, V6, V7 - KT88 McIntosh Part No.165073
Note: Because of the high voltage involved with all vacuum
tubes, they should only be replaced by an authorized
McIntosh dealer or service agency.