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11. 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.
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 elec-
tronic 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. You can confirm this fault
using the bias display LEDs - no amount of adjustment will be able to extinguish the minus
LED.
3. Internal short circuit: normally, the electronic protection cuts in and the red "off" LED
il-
luminates, or the tube will not respond to bias adjustment (the display keeps returning
to
the red area).
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 dis-
tortion 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, but these will not harm the amplifier.
4.
Is there a loss of sound quality as tubes age?
No. Tubes normally sound the same throughout their life. Our soft-start technology contributes
greatly to extending the service life of tubes. You can tell when an output tube has reached the
end of its useful life: it becomes impossible to adjust it correctly. Driver tubes cannot be
checked, but these will generally last for well over 10 years.
5.
Does the power amplifier have to have all tubes fitted?
Theoretically, the power amplifiers will operate without any tubes at all. For test purposes, or
as a temporary measure, you can operate a power amplifier with less than a full complement
of output tubes. Of course, its power output will be reduced, but the amplifier will come to no
harm if it is operated continuously like this.
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.
You will find examples of such loudspeakers from companies such as: Magnepan, Isophon,
Martin Logan, etc.
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