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Pre-amp tubes don't normally wear out as a rule. Therefore, it is not a good idea to change them just for the
sake of changing them. If there isn't a problem - don't fix it. If there is no result from your substitutions, it may be
possible that you have more than one problematic tube. Though rare, this does happen and though it makes
the troubleshooting process a little more intimidating, it is still possible to cure the problem yourself.
NOTE: It is normal to hear a slight metallic ringing sound when tapping on the preamp tubes. As long as the
tube does not break into oscillation or start crackling or any other form of bizarre noise, it is considered normal
and functional.
TUBE NOISE & MICROPHONICS
You may occasionally experience some form of tube noise or microphonics. Certainly no cause for alarm,
this quirky behavior comes with the territory and the tone. Much like changing a light bulb, you don't need a
technician to cure these types of minor user serviceable annoyances and in fact, you'll be amazed at how easy
it is to cure tube problems...by simply swapping out a pre-amp or power tube!
First may we suggest that you set the amplifier up on something so that you can get to the tubes comfortably
without having to bend down. It also helps to have adequate lighting as you will need to see the tube sockets
clearly to swap tubes. Use caution and common sense when touching the tubes after the amplifier has been
on as they may be extremely hot! If they are hot and you don't want to wait for them to cool off, try grasping
them with a rag and also note that the glass down around the bulbous silvery tip is considerably less hot which
makes it easier to handle. Gently rock the tube back and forth as you pull it away from its socket.
DIAGNOSING POWER TUBE FAILURE
There are two main types of tube faults: shorts and noise. Both large and small tubes may fall prey to either of
these problems but diagnosis and remedy is usually simple.
If a fuse blows, the problem is most likely a shorted power tube and shorts can either be mild or severe. In a
mildly shorted tube the electron flow has overcome the control grid and excess current flows to the plate. You
will usually hear the amp become distorted and begin to hum slightly. If this occurs, quickly look at the power
tubes as you switch the amp to STANDBY and try to identify one as glowing red hot. It is likely that two of a
pair will be glowing since the "shorted" tube will pull down the bias for its adjacent mates, but one tube may
be glowing hotter — and that one is the culprit. The other two are often fine — unless they've been glowing
bright red for several minutes.
Because there is no physical short inside the tube (just electrons rioting out of control) merely switching to
STANDBY for a few moments then back to ON will usually cure the problem...at least temporarily. Watch the
tubes carefully now. Should the problem recur, the intermittent tube will visibly start to over heat before the
others and thus it can be identified. It should be replaced with one from the same color batch, shown on its
label. Call us and we will send one out to you.
The severe short is not nearly so benign. In the worst cases, a major arcing short occurs between the plate
and the cathode with visible lightning inside the glass and a major noise through the speaker. If this is seen to
happen, IMMEDIATELY turn the amp to STANDBY. By this time the fuse probably will have blown. Such a short
is usually caused by a physical breakdown inside the tube including contaminate coming loose or physical
contact (or near contact) between the elements. Replace it and the fuse with the proper slo-blo type and
power up the amp using the power up procedure as we described earlier in this manual.
TUBE NOISE
Often caused by contamination within in a tube, the culprit can usually be identified, and by lightly tapping on
the glass, you will probably hear the noise change. Hearing some noise through the speakers while tapping
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