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Important Information About Tubes and Tube Products (continued):
The Importance Of Proper Biasing:
For.the.best.performance.and.longest.tube.life,.proper.biasing.is.imperative..Bias.is.the.nega-
tive.voltage.which.is.applied.to.the.power.tube's.control.grid.to.set.the.level.of.idle.current..
We.cannot.over.emphasize.the.difference.in.warmth.of.tone.and.dynamic.response.that.come.
with.proper.biasing..If.the.bias.is.set.too.high.(over.biased),.the.sound.from.the.amp.will.be.
distorted.at.all.levels..If.the.bias.is.set.too.low,.(under.biased).the.power.tubes.will.run.hot.(the.
plates.inside.the.tubes.may.glow.red.due.to.excessive.heat).and.the.sound.from.the.amplifier.
will.lack.power.and.punch..The.excessive.heat.greatly.reduces.tube.life.–.from.a.few.days.to.
as.little.as.a.few.hours.in.extreme.cases..Setting.the.bias.on.your.amp.is.like.setting.the.idle.
on.your.car..If.it's.too.high.or.hot.it's.running.away.with.you.and.if.it's.too.low.or.cold.it.will.
choke.when.you.step.on.it.
The.bias.is.adjusted.at.the.factory.in.accordance.with.the.type.of.power.tube(s).installed.in.
your.amplifier..It.is.important.to.point.out.that.tubes.of.the.same.type.and.specification.typi-
cally.exhibit.different.performance.characteristics..Consequently,.whenever.power.tubes.are.
replaced,.the.bias.voltage.must.be.checked.(unless.the.amplifier.is.equipped.with."self-biasing".
circuitry).and.readjusted.to.accommodate.the.operating.parameters.of.the.replacement.tubes.
Depending.on.the.model.and.amplifier.type,.there.may.be.hum.balance.controls,.trim.pots,.or.
bias.adjustment.controls.on.its.rear.panel..However,.the.bias.adjustment.should.be.performed.
only.by.qualified.service.personnel.with.the.proper,.calibrated.test.equipment.
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