1. First make sure the Tube Selector switch located in the Tube Bias section matches the tube type installed. Then
with the Master Volume turned all the way down turn the Power switch ON leaving the Standby switch in
the Standby position.
2. Set your test meter to read DC voltage. Then place the negative (black) lead of your meter into the black Test
Point located in the Tube Bias section on the rear panel. Then place the positive (red) lead of your meter into the
red Test Point. Depending on the size of your test leads you may have to hold them in the Test Points to assure a
good connection.
3. After the tubes have warmed up for about a minute turn the Standby switch to the Operate position and read the
voltage on your meter. With a small screwdriver you will need to adjust the Bias Adjust trim pot located
just below the Test Points so that your meter reads about 0.600 volts if you are using EL34 tubes
and about 0.450 volts if you are using 6L6 tubes. Turning the Bias Adjust trim pot clockwise will increase
the voltage and turning it counterclockwise will decrease the voltage.
4. After initially setting the bias allow your amp to warm up for about 5 more minutes then retest and readjust the
bias as indicated above. Exact readings are not critical and some uctuation is normal. Just try to get as close to
the target voltage as possible.
5. Your amp is now biased and ready to play!
Tube Bias Background Information All ampli ers (solid-state or tube) require bias to work properly. In a single ended
ampli er, the requirements are simple in that the tube should be biased or operated so that with no signal present, DC
current should ow through the output stage (tube and transformer) at approximately 1/2 the maximum design value.
When the signal transitions positive the current increases from the quiescent position and when the signal transitions
negative the current decreases from the quiescent position. So you can see that if there was no bias, there would be no
quiescent current, thus no way to operate properly for the negative going portion of the signal, limiting the negative side
of the waveform. Too much bias would limit the amount of current you could add for positive going signals, limiting that
side of the waveform.
For a push-pull output stage (tube amps), the scenario is different, since one tube ampli es the positive going portion
of the signal and the other tube ampli es the negative going portion of the signal. In fact, if the world was perfect, we
would need no bias since the positive side of zero would be handled completely by one tube and the negative side of zero
would be handled completely by the other tube. This would be the proper de nition of class B operation. Since tubes
are not perfect devices, the transition at zero is not very linearthis is as one tube turns off, the other tube may not be
quite ready to turn on. This can lead to a discontinuity of the signal around zero which is the worst possible place for it to
occuras it is highly audible and rather ugly sounding. The solution once again is to bias both tubes slightly on to allow
for a more graceful handoff between the positive and negative sides of the signal, called AB operation. This is done by
adjusting the bias just enough to achieve the necessary results. Too much bias and current will be wasted as heat
dissipated within the power tubes and output transformer greatly shortening your power tubes useful life. Too little bias
may give the amp a cold, grainy texture.
WARNINGS:
POWER TUBES BECOME VERY HOT AFTER BEING USED.
NEVER CHANGE THE POWER TUBES UNTIL THEY HAVE COOLED FOR AT LEAST 15 MINUTES.
NEVER CHANGE THE TUBES WITH THE AMP ON!!!
GETTING STARTED:
Since your EL DIABLO 100 ships with all tubes installed and the ampli er fully tested, biased and burned-in at the
factory, the user set-up is quite simple.
Un-box your EL DIABLO and verify that the AC input input voltage selector switch matches the power in your area. The
EL DIABLO ships from the factory with the switch set to 115 volts.
Verify that you have the correct mains cord-set for your area. This piece of information is primarily for our international
customers who may have a choice of power receptacles in their country.
Make sure to send in your warranty registration card.
Read your owner?s manual. There is valuable information and safety tips in this manual and the knowledge you learn
here will translate into enjoyable quality tone for years to come.
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