Palmer FAT50 Handbuch Seite 16

5 Tube rePLaCeMeNT & MAINTENANCE:
The FAT50 uses carefully selected 5881(6L6GC) and 12AX7 tubes. After the burn-in their electrical values and
mechanics are evaluated (they must be free from microphonics) and, finally, their sound characteristics are
checked in a real world situation with each amp. Matching the power tubes is one of the most important steps for
consistent, reliable operation.
wHY aND wHeN SHouLD TubeS be rePLaCeD?
The tubes used in each FAT50 are high quality long-life tubes exclusively. Make sure to check the following before
replacing tubes:
Is it the tube or something else – a faulty speaker cable might be the reason for blown power tubes. This might
cause the replacements to blow as well.
Has the mains voltage been consistent – a power surge might have caused the tubes to blow (also, generators
don't always supply constant voltages).
Has a fuse blown while the tubes are in perfect working order – old fuses, partial discharge within the tube, or
arcing caused by spikes might be the reason. In this case there is no need for replacement.
However, tubes do wear out after various periods of time. This is indicated by microphonics, hum, loss of high
frequency response and power necessitating replacement.
Caution: Do not replace tubes for the sake of experimentation to prevent damage to your FAT50 and costly repairs!
How SHouLD TubeS be rePLaCeD?
Tubes should be replaced by qualified personnel only. Disconnect the power plug from the mains outlet, and let the
power capacitors discharge for a minimum of 2 minutes before removing the safety grille on the rear of the amp.
Pull the tube carefully from its socket. Replace a single power tube with a tube of identical ratings only matching
the remaining tube. Replacing the set of power tubes requires bias adjustment if the ratings of the new set vary
from the previous tubes. Due to the knowledge and skills needed bias adjustment should be performed by a
qualified technician only.
How CaN Tube LiFe be eXTeNDeD?
Do not operate the FAT50 without a load, i.e. a loudspeaker! Use a rugged, high quality loudspeaker cable.
Always use the Standby switch. Frequent heating increases wear while switching off the anode voltage (this is
what the standby function does) keeps the tubes at operating temperature, but idle!
Avoid vibration and shock, especially when operating the amp. After turning it off, let the amp cool down before
transport.
Accurate bias and hum balance adjustment prolong tube life. These settings should be checked if tubes wear out
quickly.
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