Octave JUBILEE MONO SE, Owner'S Manual

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10. FAQ
1. Can you operate the amplifier when no
loudspeakers are connected?
Yes. All OCTAVE amplifiers are protected
against open circuit conditions, i.e. they will
not be damaged if operated with the
loudspeakers
disconnected. However,
when connecting your loudspeakers to the
amplifier, you should set the volume control
on your preamp to 0 to avoid excessive
output to the speakers. Protected against
open circuit conditions here means without
any speakers or speaker cable connected.
If you use a "high capacitance" speaker
cable, you should make sure that you
connect the cable first to the speakers and
then to the amplifier.
2. Can a short circuit on the speaker
outputs damage the amplifier?
At low levels, the power amplifier is
absolutely short-circuit proof. At higher
levels, the electronic protection is activated.
Under normal circumstances, a short circuit
condition at the speaker outputs will not
damage the amplifier.
3. How do you recognize a faulty tube?
There are 3 different symptoms indicating a
faulty tube:
1. Broken heater filament: the tube stops
glowing
2. Defective cathode layer: the tube glows,
but no current can flow. This fault will
be shown on the bias display.
3. Short circuit within the tube: This fault
will normally trip the electronic
protection and cause the red OFF LED
to illuminate.
With faults 1 and 2, the amplifier will still
operate, although the channel containing
the faulty tube will be quieter than normal.
At low listening levels, the fault may not be
obvious, but distortion will become evident
at higher listening levels.
If fault 3 occurs, the protection circuits will
normally switch the amplifier off. You may
also hear loud background noises just
before it switches off, although these will
not harm the amplifier. (See chap. 7.2.)
4. Is there a loss of sound quality as tubes
age?
No. Tubes normally sound the same
throughout their service life.
Our soft-start technology contributes
greatly to extending the service life of
tubes. You can see when an output tube
has reached the end of its useful life: it
becomes impossible to adjust its bias
correct. Driver tubes cannot be checked,
but these will generally last for well over 10
years.
5. Does the power amplifier have to have
all power tubes fitted?
No. The power amplifiers have been
designed to operate without a full
complement of output tubes for test
purposes, or as an interim measure. Power
output will, of course, be reduced.
Normally, operating the amplifier like this
for extended periods will not result in any
damage. However, you must not try to run
the amplifier at full power.
6. What is the significance of
loudspeaker impedance and
efficiency?
The impedance and efficiency of modern
loudspeakers is not an issue for OCTAVE
amplifiers. The often-quoted damping
factor is not normally a guarantee that an
amplifier will exert tight control over the
loudspeakers. In practice, speakers of
85dB efficiency and above are suitable for
use with tube amplifiers. The high stability
of the OCTAVE power amplifier technology
even allows the use of speakers whose
impedance dips as low as 2 ohms.
7. What cables are suitable for tube power
amplifiers?
The cable manufacturers are now offering
cables that have supposedly been
designed specifically for tube amplifiers.
Although such cables may be of good
quality, there is no need to use special
cables with tube amplifiers. Speaker cable
can exhibit high values of capacitance and
inductance. Tube power amplifiers deal
with such loads better than transistor power
amplifiers. The only exception would be in
the case of tube preamp to power amp
interconnect cable longer than 5 meters. In
this instance, a low capacitance cable is
advisable.