Owner`s manual

PAGE 8

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 swap-

ping 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 intermit-

tent 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 on the 12AX7’s is normal however. And

the one nearer the INPUT will always sound louder because its output is being further ampliﬁed by the second 12AX7.

The power tubes should be all but quiet when they are tapped. If crackling or hissing changes with the tapping, you have probably found

the problem. To conﬁrm a noisy power tube, merely put the Road King on Standby, remove it from its socket and turn it back on. It will

cause no damage to run the Road King brieﬂy with one power tube missing. You may notice a slight background hum, however, as the

push-pull becomes unbalanced. Whenever you are trying to diagnose a suspect tube, keep your other hand on the POWER and STANDBY

switches ready to shut them off instantly in the unlikely case you provoke a major short.

If you think you’ve located a problem tube but aren’t sure, we recommend substituting the suspect with a new one just to be sure of your

diagnoses. You will be doing yourself and us a big favor by just following the simple guidelines previously mentioned regarding tube re-

placement. You’ll probably be successful with much less effort than is required to disconnect everything and haul the unit to a technician

who will basically perform the same simple tests. If the tubes are still within their six-month warranty period, we will happily send you a

replacement. Just note the color designation on the tube label so that we can send you the appropriate match.