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Appendix C: Maintenance
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a
PPendiX
C: m
aintenanCe
The Spider Valve MkII 112 and 212 combo amps include two 12AX7-B preamp tubes and
two matched 5881 (6L6) power amp tubes. The Spider Valve MkII HD100 head features
two 12AX7-B preamp tubes and four matched 5881 (6L6) power amp tubes.
Keep in mind that tubes are like car tires – they get worn out through use and need to be
replaced. How loud you play and how long you play affects how often you need to re-tube
your amp. If you play a lot, changing the power tubes once a year is normal. Preamp tubes
can often last twice as long, even longer.
For the 12AX7-B preamp tubes, we recommend that you always change both tubes at the
same time, since one bad tube can often “take down” a good tube.
When changing power tubes, you must only use matched sets of 5881 (6L6) tubes and
have them properly biased for optimum tone and tube life.
Tube Troubleshooting
Most amp problems (squeals, crackling, low power, mushy bass response, etc.) can be
traced to bad or weak tubes. If you hear your sound begin to deteriorate, it may be time to
change your tubes. Here are some possible signs:
• Dull or cloudy sound, despite your tone settings
• Loss of low-end response
• Uneven tonal output – some notes seem louder than others
• Amp becomes noisy
• Amp sounds thin
• Amp feels weak or has low output
• Amp has fluctuating power output
• Output decays quickly – isn’t able to produce your guitar’s sustaining notes
• Popping sound accompanied by intermittent light from tubes
• The appearance of “white frost” inside the tube – (this usually means the tube has
cracked and must be replaced)