Owner`s manual

Guitar AmplifierGVT5H
8
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Important Information About Tubes (continued):
Whenever you replace the power tube(s):
Check the preamplifier tubes for microphonics by turning the amplifier on, turning up the gain
and tapping lightly on each tube with the end of a pencil or a chopstick (my favorite). You will
be able to hear the tapping through the speakers, which is normal. It is not normal for a tube
to ring like a bell after it’s tapped. If it does ring, then it’s microphonic and should be replaced.
Remember to use only high-quality, low microphonic tubes in the preamplifier section.
Even though power tubes are rarely microphonic, they should be checked, anyway. Power
tubes may be checked for microphonics in the same fashion as the preamp tubes.
The amount of noise generated in very high gain amps may be reduced simply by swapping
the preamp tubes around.