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PHANTOM OWNER’S MANUAL (rev.2) PAGE 16 OF 17
or microphonic tube in this position will affect the entire amp. Microphonic or noisy tubes in
several other positions may not be audible at all. You can try tapping the tubes like you did
the power tubes and see if the problem worsens. It is normal to hear a slight ring when you
tap on preamp tubes. This test is only to see if the identified problem changes when tapping.
This test is NOT outcome determinative.
If the problem is only on one channel or the other, you’ll know which tube is the problem. If
it’s only on the clean channel, it’s tube V2. If it’s on the crunch channel, it is either V3 or V4,
but most likely V3. NOTE: V1 usually is the culprit. Even if you don’t hear it on both
channels, you should check V1 anyway. Tube problems are much more dramatic on
V1 than any other position. When you think you have determined the culprit, put the amp
on standby and change that tube. Retest.
NOTE: It is always advisable to change preamp tubes one at a time. It is a good idea
to keep at least one known good preamp tube for this purpose. Then you will know for
sure if you have found the problem.