Palmer FAB5 Bedienungsanleitung Seite 12

5) TUBE REPLACEMENT, MAINTENANCE, AND CARE
After "burn-in" (initial operation under load) the tubes used in the FAB5
undergo a sophisticated selection process in which their electrical speci-
fications and mechanical characteristics (microphonics) are tested. Ad-
ditionally, their tone behaviour is tested in an acoustical test in the
finished equipment.
WHEN DOES IT MAKE SENSE TO REPLACE TUBES?
The tubes used in the FAB5 stand out because of exemplary workmanship and
long service life. If a problem should nevertheless occur, before replacing
the tubes, you should first please ask yourself the following questions:
Was the fault or failure caused by the tube itself or perhaps by a periph-
eral device, e.g., a defective speaker cable as the cause for defective
power tubes? (If the defect is not remedied, the problem could reoccur af-
ter the tube replacement.)
Was the mains voltage constant during operation? With all-tube amplifiers,
a breakdown can be caused by a mains voltage surge. Surges occur, e.g.,
with generators or faulty high-voltage circuits.
Is it possible that merely a circuit breaker/fuse has been tripped without
there being a real defect? "Old" circuit breakers/fuses, tube de-ioniza-
tion, or arcing due to voltage peaks could be the cause. Then it would make
little sense to replace the tubes. After being used for a certain amount of
time, tubes evidence signs of fatigue (increased microphonics, susceptibil-
ity to hum, loss of treble, reduced output, etc.). Signs like this neces-
sitate replacement, because they not only lead to decreased sound quality,
but also indicate that the affected tubes are about to fail.
Note: replacing tubes for experimentation purposes is a bad idea. The re-
sulting costs in the event of improper actions can be surprisingly high.
WHAT IS IMPORTANT TO KEEP IN MIND WHEN REPLACING TUBES?
Tube replacements should be left to qualified professionals. Before remov-
ing the rear panel, the mains plug of the FAB5 must be unplugged and the
equipment must be allowed to discharge for a minimum period of 2 minutes.
Loosen the rear panel screws and pull them out together with the electron-
ics chassis. Take care of the speaker connection when doing so. Now the
tubes can be removed carefully from their sockets. No bias adjustment is
required when replacing power tubes.
IMPORTANT: THERE MUST BE A TUBE IN EVERY TUBE SOCKET!
HOW CAN TUBE SERVICE LIFE BE EXTENDED?
Never operate the FAB5 without a load (speaker)! Thus a high-quality, kink-
proof speaker cable is absolutely necessary if you want to connect an ex-
ternal speaker.
Avoid vibration, especially when the equipment is on. Before transport,
turn the amp off and let the tubes cool down.
12