When to Replace Tubes | Hughes & Kettner TrilogyTM manual

Trilogy™ Manual 1.1

Replacing Tubes,

5 Service and

preventive Maintenance

TRILOGY™ is factory-loaded with EL34 and 12AX7 tubes. Once they’ve been burned in – that is, operated continuously under a load – they are subjected to a rigorous selection process. Their electrical specs and mechanical status (microphonics) are checked, and then they are installed in an amp and sound- checked. One of the most important steps in this process is tube matching, whereby tubes with the same characteristics are teamed up in matched sets of power tubes.

5.1 When to Replace Tubes

The tubes in TRILOGY™ are exemplary in terms of quality, workmanship and long service life. In the unlikely event that you encounter a problem, please run down the following checklist before you swap your old tubes for a new set:

Was the fault or failure of the power tube caused by the tube itself or by a flawed peripheral device or component, perhaps a defective speaker cable? (If you don’t get to the bottom of the problem and remedy it, it may crop up again even after you replace the tubes.)

Did the mains voltage fluctuate or spike while the amp was on? In all-tube amps, over-voltage surges in the mains net can certainly cause drop-outs. Over-voltages are often caused by generators and faulty high-current power circuits. Perhaps a fuse blew even though none of the tubes is actually defective? An old fuse, tube de-ionization or mains voltage power surges may have triggered the fuse. In this case, replacing tubes is a waste of money, time and effort.

Tubes show definite signs of wear when their service life is nearing its end. Telltale signs are increased microphonics, noise and hiss, muddier tone through loss of high-end frequencies, degraded performance, etc. Take these indications seriously and replace old tubes. Not only do these side effects take their toll on sound quality, they also indicate the aging tube will soon fail!

xNote:

Replacing tubes for experimentation purposes is not recom- mended. Installing the wrong tubes will damage the amp and cost you a lot more than you bargained for in repair costs.

5.2 Things to Bear in Mind When Replacing Tubes

The golden rule is that replacing tubes is a job best left to qualified professionals. Accordingly, the following guidelines are addressed and apply to qualified service technicians only:

Pull TRILOGY™’s mains plug and allow for a discharge time of at least two minutes before removing the chassis from the rear of the amp. Once the chassis has been removed, carefully ease the tubes out of their sockets. A single power tube may only be replaced if the replacement tube precisely matches the original, that is, the old and new tubes’ characteristics are identical. As a rule, use matched sets only when replacing power tubes. When a new set of power tubes with characteristics identical to the old set is installed, it is not absolutely necessary to re-bias the amp. However, the amp must be biased when

a replacements set’s characteristics do not match the original set’s. This requires experience and extensive working know- ledge in measuring techniques, which is why this is a job for qualified technicians with tube amp tuning experience.

5.3 How to Prolong Tube Life

•Never operate Trilogy™ without connecting a load (loud- speaker)! To this end, always use high-quality, heavy-duty speaker cords that won’t crimp.

•Use the STANDBY switch! Heating up tubes frequently shortens tube life. Cut anode voltage using the STANDBY function to decrease operating hours and extend tube life.

•Avoid exposing the amp to vibrations, especially when it’s powered up. Switch the amp off well before transporting it to allow tubes to cool off completely.

•Make sure all peripheral devices and connecting cords are in a state of good repair! Ensure air can circulate freely around the amp’s ventilation slots at all timesæyour Trilogy™’s life depends on it.

•Never expose the amp to extreme heat, heavy dust and, par- ticularly, moisture.

•Always check peripheral gear’s specs to ensure these accessories are suitable for the amp. Never connect speaker cabinets with an impedance (ohm) rating lower than Trilogy™ is designed to handle.

•Never connect devices with high output signal levels (e.g. power amps) to Trilogy™’s input.

•Check the mains power rating before plugging the amp in. When in doubt ask the venue’s sound technician or facility engineer.

•Refrain from DIY repairs! Also have a qualified technician replace internal fuses.