Brunetti PIRATA 141, Руководство пользователя, Страница: 16 / 19

PREAMP TUBES
The preamp tubes are used to preamplifier the signal. They usually last the entire life of the amplifier.
The possible problems of these kind of tubes are: microphonics and noise.
Microphonics
The microphonics is the ability of a tube to reproduce external vibrations further the signal.
This phenomenon can be much more evident in high gain stage like the distortion channels.
Lightly tapping on the glass side of the preamp tubes, while the head is on, you' ll hear a stroke through the
speaker, this is normal don' t worry.
But if you hear hi frequencies (ringing or squealing) and in some case a distorted sound, it means that the tube is
microphonics.
You will note that the first tube is more subject to reproduce this stroke more than the others, because it' s at
the begin of the preamplification chain.
Noise
Tube has an own intrinsic floor noise that comes from its work and construction.
During tube life this noise may increase creating a sort of a ringing or squealing.
In these two cases, you have to find the defective tube and repleace it with a new one.
The preamp tube doesn't need to be selected, (normally this control has been made by the constructor), but be sure
to replace with good quality tubes.
We suggest thay you use tubes of same brand and model.
POWER TUBES
Power tubes are the last amplification stage before the out trasformer and speaker out, and they can get exhausted.
Normally a power tube working in A/B class lasts 800 - 1000 hours. It depends also on the volume used.
In an amplifier with same power, in A class, the tube lasts 600 - 800 hours. In this class work tubes are more stressed.
When replace power tubes
You can recognize an exhausted tube because there's a loss of power and volume. Sound has not the same impact,
in particular on low frequencies.
Main faults on this kind of tube are :
- short inside the tube. In this case normally the HT fuse will blow.
- tube light off. It's easy to recognize this problem tube because you can't see any light inside the tube.
- tube become glowing. In this case there's an increase of noise (hum) and sound will be distorted.
In all the above cases tubes can' t be fixed, and have to be replaced.
If the problem tube has worked more that 1 year, we suggest that you replace all power tubes, this to guarantee the
best performance of your amp.
If the problem tube has less than 1 year you can replace only that one.
Warning!!
You have to mount only selected and matched tubes, with the same
characteristics of the tube supplied on your
aplifier. See the ''Matching Reference'' label on the tube.
If you mount tubes with different ''Matching Reference'' is necessary to adjust the Bias, to let the amp work properly.
GENERAL INFORMATION
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