8
To turn it back on, press and hold any of the source buttons except “5” (that is, MUTE or 1-4) while
pressing the ON-OFF button. The red ON-OFF switch will flash four times quickly to indicate that
automatic-power-off has been enabled.
The automatic-power-off setting cannot be disabled in high-bias mode. If you disable it, the amplifier
will place itself in normal bias mode.
The Minotaur should not be left running when not in use. Turning it off prolongs tube life and saves
power. If the amplifier is used regularly, the vacuum tubes stabilize within minutes of turn-on.
4.3
V
ENTILATION AND
C
HASSIS
T
EMPERATURE
Some people are surprised that vacuum tubes generate heat. The Minotaur is designed to dissipate heat
by having air flow in underneath the chassis and out through the top. If there is not enough air space
above the amplifier (at least 4 inches), or if the top or bottom ventilation slots are blocked, or if the
amplifier is placed in an enclosed space where little air can circulate, the amplifier will get quite warm
and may overheat.
Bias Mode
Expected Temperature Rise
Above Ambient With Adequate
Ventilation
Expected Maximum External
Cabinet Temperature,
Assuming 80°F (27°C) Ambient
Normal
30 - 35°F (16 - 19°C)
115°F (46°C)
High
35 - 40°F (19 - 22°C)
120°F (49°C)
In high-bias mode, with adequate ventilation and an 80°F (27°C) ambient, the external cabinet may
reach 120°F (49°C) above the tubes and heatsink. That is a very hot day in Phoenix, but not a contact
hazard, nor even uncomfortable to touch. If you notice the amplifier becoming uncomfortably warm to
touch (50°C or more), you should consider if the ventilation can be improved. If you use an equipment
rack, be sure it provides for ventilation. If you want the amplifier to run cooler, run it in normal bias
mode (see Section 4.1). And note (somewhat obviously) that if ambient temperatures are cooler, the
amplifier will be correspondingly cooler.
If internal temperatures rise too much, the system microcontroller will first turn on a fan to cool the
heatsink. Next, it will force the amplifier out of high-bias mode. Finally, the amplifier may shut down
with a FAULT indication (see Section 4.4).
