Hughes & Kettner Tube 50 User Manual download pdf (Page 13)

TUBE 50/100 - MANUAL

ENGLISH

4.0 REPLACING TUBES, SERVICE AND

PREVENTIVE MAINTENANCE

Your TUBE 50 / TUBE 100 features factory-equipped EL34 and

12AX7A Hughes & Kettner tubes. Hughes & Kettner tubes are first

burned in and then checked for their electrical and mechanical

properties (microphonics), selected and matched, and then given a

final audio and response test once they have been installed in the

amplifier.

One of the most important steps in the testing process is power

tube matching, i.e. selecting and pairing tubes with identical cha-

racteristics.

When should you replace tubes?

The tubes in your TUBE 50 / TUBE 100 are of an exceptionally

high quality and will last extremely long. If you do encounter a

problem, first check whether one of the following situations apply:

• Is the defect a problem caused by a defective or worn-out tube,

or is there actually a peripheral problem, for instance a defective

speaker cable that caused damage to the tube? If this is the case,

unless you correct the defect first, the problem will recur once

you have installed a new tube.

• Did the AC power supply fluctuate during operation? Whereas

digital equipment often malfunctions when the power supply

dips below a minimum value, all-tube amps tend to malfunction

when the power level rises above a certain value. Generators

and faulty high-power circuits often cause these power fluctuati-

ons.

• Did a fuse trip although there was no plausible cause? Aging

fuses, particle ionization in the tube or arcing due to power spi-

kes may cause this type of problem. In this case, replacing a

tube will not solve the problem.

• Old tubes begin to show signs of wear after they have been in

operation for a very long time: increased microphonics and

noise, treble loss, weak power output, muddy sound, etc., are all

indicators of pending tube failure. Power amp tubes wear out

faster than preamp tubes. If you encounter these problems,

replace the tubes. Not only do old tubes sound bad, they also

have a tendency to fail altogether.

NOTE: We recommend you refrain from exchanging tubes solely

for sound experimentation purposes. Improper use runs the risk

of damaging your amp and will not be covered under warranty.

Besides, we tested every conceivable tube option and installed

the tube types that deliver the best possible performance.

Keep the following in mind when you are ready to replace tubes:

• We recommend only qualified service personnel replace tubes.

• It is normal for all POWER TUBE STATUS LEDs to illuminate at

once briefly in response to your picking attack at higher volu-

mes. This indicates the tubes are operating properly.

• If one of these LEDs illuminates continually, then the correspon-

ding power tube is defective (cathode short) and the tube and

the corresponding fuse must be replaced. Note that POWER

TUBE STATUS LEDs indicate a cathode short only, and no other

power tube defect. Ensure you also check the ANODE fuse! If a

replacement fuse trips shortly after it has been installed, then one

of the power tubes is defective even if the POWER TUBE STA-

TUS LED does not illuminate to indicate a cathode short.

• At higher volumes, the amp is operating properly when all

POWER TUBE STATUS LEDs illuminate at once briefly in res-

ponse to your picking attack. If one of the LEDs does not illumi-

nate along with the others, this may indicate a defective tube or

a faulty contact at the tube socket.

• The mains cord must be unplugged from the wall socket before

the POWER TUBE PANEL is removed! A power down interval of

at least two minutes is mandatory. Once the panel has been

removed, the tubes can then be carefully removed from their

sockets. At this point the cathode fuses are also accessible. A

single power tube may only be replaced with a tube that has

identical specs.

• Use only matched pairs of power amp tubes.

• If you install a matched pair of tubes bearing precisely the same

specs as the original tubes, the amp does not have to be re-bia-

sed. Conversely, if the specs are not identical, the amp must be

biased. Biasing is a complex procedure requiring special tools

and should only be executed by a qualified amp technician.

The chassis must be removed to replace preamp tubes.

How can you extend the life of your tubes?

• Never operate your TUBE 50 / TUBE 100 without a proper load

(speaker) connected to the output. A high-quality, heavy-duty

speaker cable is absolutely essential for the protection of your

amp!

• Use the STANDBY SWITCH! The more often the tubes are hea-

ted up, the shorter their life span will be. The standby feature

switches the anode voltage off and lengthens tube life by mini-

mizing wear and tear.

• Switch the amp off and let the tubes cool down before transport.

A quality flight case is a good investment and is only slightly

more expensive than a complete set of tubes.

• Proper bias and trim extends tube life. If you find the tubes need

to be replaced too often, consult a qualified technician.

All other TUBE Series Amp components do not require maintenan-

ce. Use a slightly dampened cloth to clean all metal parts and the

exterior surfaces. Avoid exposure to mechanical shocks, extreme

heat, dust and moisture. Ensure the cooling vents are not obstruc-

ted during operation.

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Hughes & Kettner Tube 50 User Manual Page 13

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