Palmer PDREI Manuel D'utilisation page 18

8) TUBE REPLACEMENT AND MAINTENANCE
The DREI uses carefully selected tubes. After the burn-in their elec-
trical values and mechanics are evaluated (they must be free from micro-
phonics) and, finally, their sound characteristics are checked in a real
world situation with each amp.
WHY AND WHEN SHOULD TUBES BE REPLACED?
The tubes used in each DREI 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 volt-
ages).
Has a fuse blown while the tubes are in perfect working order – old fus-
es, 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 indi-
cated 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 DREI and costly repairs!
HOW SHOULD TUBES BE REPLACED?
Tubes should be replaced by qualified personnel only. Disconnect the pow-
er plug from the mains outlet, and let the power capacitors discharge for
a minimum of 2 minutes before opening the safety grille on the rear of
the amp. Pull the tube carefully from its socket. When replacing tubes,
no Bias adjustment is necessary! All three power amplifiers must have a
tube!
HOW CAN TUBE LIFE BE ExTENDED?
Do not operate the DREI 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 turn-
ing it off, let the amp cool down before transport.
Accurate bias and hum balance adjustment prolong tube life. These set-
tings should be checked if tubes wear out quickly.
THESE ARE SOME BASIC RULES TO MAINTAIN YOUR DREI IN PERFECT WORKING ORDER:
• A quick move from cold to warm locations may result in condensation
inside the amp. Let the amp warm up to room temperature before switching
it on.
• Make sure the equipment connected to your DREI is in perfect order.
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