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1) When do I have to replace the power tubes?
During their life the power tubes loose their sound and power characteristics. You can recognize an exhausted tube because it usually has less power and less “impact” especially in the low frequencies. Another typical characteristic of an exhausted tube is the presence of strange burning on the external bulb.

2) How long does usually a power tube last?
The power tubes life is usually connected to the volume used while playing and to the tube amplifier working time. Another important feature is the output stage configuration: if an amplifier works in Class A, the tubes usually have to stand more “stress” and their lifetime will be shorter. So, according to the different uses, a power tube can last 800 / 1.000 hours approximately.

3) Can I personally replace my amplifier power tubes?
We don’t recommend it. Each tube has its own amplification “value”. When replacing the power tubes, you must be sure that the new ones are selected or “MATCHED”, i.e. that they have the same “value”. So, in case the faulty tubes are mounted in an amplifier with a regulating BIAS, it’s better to reset it. An incorrect BIAS regulation can cause the unit bad working.

4) Can I replace the power tubes with different kind of tubes? And which results do I obtain? Ex: EL34 with 6L6 or vice-versa.
It’s possible to replace 6L6 tubes with EL34 tubes or vice-versa only if you regulate the BIAS in the correct way but the result are not always the best. The problem is the output transformer which is not the same for the two types of tubes: replacing 6L6 tubes with EL34 tubes and vice-versa creates a lack of power which sometimes can be useful but in general it’s a lack of volume of the 30%.

5) How long does usually a power tube last?
The preamplifier tubes can last for all the amplifier life. The preamplifier tubes are often changed to have different sound characteristics and not because they are exhausted. The preamplifier tubes replacement influences the sound more than the power tubes replacement.

6) When is a preamplifier tube microphonic?
A preamplifier tube is microphonic or has become microphonic when it reproduces external vibrations. The amplified vibrations create a distortion which can be often heard by the listener. This problem becomes more evident in a high gain stage (feedback).


7) How do I have to connect my XL head to the 4×12″ XL-Cab?
In order to connect the XL head to the 4×12″ XL-Cab, you have to place the XL impedance selector on 16 Ohm. Then, you have to select the Mono use on the XL-Cab and finally connect XL head 16 Ohm to XL-Cab 16 Ohm with a power cable (do not use a signal cable!!!)

8) How do I have to connect my XL head to two 4×12″ speakers?
In order to connect two XL-Cab speakers to one XL head, you have to select the Mono use on the XL-Cab. Then plug the cables in the speakers 16 Ohm input and connect them to the two XL outputs. The XL impedance selector must be on 8 Ohm because the two speakers are parallel.


9) In order to set a rack system volume, is it better to keep the amplifier volume fixed and act on the amplifier volume or viceversa?
Both cases are possible but be careful the amplifier doesn’t reach a saturation level with a too high pre output level. In this case the result is a distorted sound even if you have selected the CLEAN channel on the preamplifier.