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13. FAQ
1.
Can you operate the V 70 SE when no loudspeakers are connected?
Yes. The V70SE, like all OCTAVE amplifiers, is fully protected against open circuit operation,
i.e. the amplifier will come to no harm if it is operated without loudspeakers connected.
2.
How do you recognize a faulty tube?
There are 3 different symptoms indicating a faulty tube:
1. A broken heater filament: the tube stops glowing.
2. A defective cathode layer: the tube glows, but no current can flow. You can confirm this
fault using the bias display LEDs – no matter how much you try to adjust the bias, the
minus LED will always remain on.
3. A short circuit inside the tube. Normally, this will cause the electronic protection to cut in
and the red "off" LED to illuminate, or else the tube will refuse to respond to bias
adjustment (the display keeps returning to the red area).
The amplifier will still operate with either of these faults present, but the channel containing
the faulty tube will be quieter than normal. The fault may not be obvious at low listening
levels 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 chapter 6.1).
3.
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 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.
4.
Does the V 70 SE have to have all of its tubes fitted?
In principle, the V 70 SE will also operate without tubes. It is sometimes useful to do this when
testing the operation of the switching functions such as the selector switch, remote control,
etc. Of course, it is not possible to play music under these circumstances.
For test purposes or as a temporary measure one channel may be fitted with just a single
power tube, although its power output will, of course, be reduced. The amplifier will come to no
harm if it is operated continuously like this.
Operation without driver tubes is also possible for test purposes, although, for obvious
reasons, music playback is not possible.
5. 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 85 dB 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.
6. 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, and tube power amplifiers deal with such loads better than
transistor power amplifiers. The only exception would be if you needed to use a tube pre-to-
power amp interconnect cable longer than 5 metres. In that case, a low capacitance cable
would be advisable.
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