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STUDY
GUIDE
Part VI
Ga zint a s and Gazoutas
B
y no w it should be o bvio us t ha t in th is
wacky wo rld of elect ron ics and ham
radio. every thing dep en ds upo n everything
else - which makes it most d iff icu lt to
name a single com ponent as " the corn ersto
ne" o n wh ich th e who le set up rests.
But were it necessary to do so , the
amplifier wo uld be a prominent candidate
for t he position. Without am plifiers,
neith er rad io nor an y o ther applicatio n of
electro nics as we know them toda y could
exist. A m plifie rs are an essential ingredient
of every osci llato r, of every transmitter,
and o f every re ceiver , a nd in th e ir absence
we co uld expect litt le more perfo rmance
than Marco ni achieved seven decade s back.
Because amplifiers are so essent ial. a
number of 'q uestio ns o n the General class
examin at io n are inte nde d to test the applicant's
k no wledge of t hem. an d ma ny
others which do no t deal o n t he sur face
wit h amplifiers as suc h neve rtheless require
a knowl ed ge of amp lifier principles to
answer.
In this chapte r, we're goi ng to di scuss
amplifiers. and co ver th e st udy list q uestions
wh ich deal d irectl y with th is subjec t.
Qu est io ns dealt with arc:
20 . What are so me possi ble causes of
excessive plate cur rent in a class C power
amplifier'!
45. List th e th ree main classe s of amplifier
ope rat io n an d ex plain the use fo r
which each class is best suite d.
62
47. What is mean t by " flat-topping" of
a single sideband signa l and what are sorne
possible causes of it?
48. What does grid current flo w in a
class A amplifier indicate?
As usua l, rat her than dealing with t hese
q uestions specifically , we'll rephrase them
into more general ones .
For a star t, let's ask " What is an
amplifie r'!" This basic know ledge will be
necessary in orde r to classify am plifiers
into th e t hree main classes.
We can continue by asking " How are
amplifiers classifie d?" This is no t ju st a
rewording of q ues tion 4 5, because a numher
of classification tec hniq ues exist, one
of wh ich has -on ly tw o main classes (and
which makes more sense in genera l than
the co nvent ional a pproac h, th ough it's no t
the an swer the FCC ex pects).
Once we kno w wha t we're talking abo ut
and ho w th ey are classi fied, we can wind
up th e discussio n on a more practical note
with " How and why do amp lifiers misbehave'?"
In getting answers to th is, we'll
co ver most of the more co m mon types of
proble ms cnco untered ,- but we hasten to
po int o ut tha t it 's im possible to cover all
the pro blems, because man y are highly
improbable an d so occur at such extende d
intervals that no one pe rso n co uld hop e to
list "ali" the po ssible troubles wit h amp lifiers
. Fortunately , a sol id kno wledge of
basic principles goes a long way toward
hel pin g cure these " rare diseases" of the
circu its .
73 MAGAZIN E