Evening star., 1926-11-14
No. SO--Condenser Caprices.

This looks like a good condenser"
Smith said, pointing to a special piece
Of equipment which he found on the
counter in a radio accessory store.
See, 1t has lots of insulation"
That started US going on the sub
1ect Of condensers and their charac-
teristics, because the best condensers
generally have the least insulation.
If the bearings Of a variable con-
denser are Of insulating material
there Is bound to be greater wear on
them and wear at this point in con-
denser Of this kind Is the prelude to
trouble. 1t throws the plates out Of
line, with the result that sooner or
later rotor plates may touch stator
plates. At any rate, the space be-
tween the plates will vary, and when
the tuning of q set is so dependent
upon the most accurate operation OF
its delicate units such variation may
mean the difference between getting
station clearly and not getting 1t at
all.
"But don't see that 1t makes much
difference whether the plates are q
little closer together at one time than
another" Smith said.
THAT is because you don't under
stani the connection between the
dieksctric and the capacity Of the
condenser replied. The narrower
the spacing between plates the
greater the capacity. other things be-
ing equal. That Is because there 10
less dielectric between the plates.
DiaIs Not Always Same.
perhaps that's why my set seems
to be so variable Of late" Smith spec
ulated.
1.-The dials are not always in the
same position for the same station.
Perhaps this happens when the rotor
plates of one Of the condensers get q
little closer or a little farther away
from the stator plates"
"That sounds reasonable" I agreed.
"But in your case l doubt very much
If the trouble Is due to bad insulation
or bearing trouble directly caused by
the bearings themselves. The con-
densers on your set are equipped with
stop, and this Is bad arrangement.
You twist the dial of one to its limit
on the marked scale and let 1t bang
on the stop. This wouldn't cause any
trouble If it happened just once in a
blue moon, but you seem to take
particular delight in letting the con-
denser rotor bang this way. That
loosens the condenser bearings and
varies the capacity Of the instruments.
"Also l was noticing that one Of
the dials scrapes a bit against the
panel. This may seem very trivial,
but that panel on your set Is too hard
to be scratched. If 1t were made OF
soma soFt material, 1t would wear
down arc thus accommodate itself to
the panel. And, of course, the dial,
in bending, carries the shaft Of the
particular condenser with It. That
throws the plates bit off, particular
ly since those stops have helped to
loosen the bearings"
wanted Smith to see that con-
densers cut up chiefly because they
are made to violate simple rules Of
radio and electricity. The capacity
OF any condenser is generally directly
proportional to the area Of the plates,
their rumber and the "dielectric con-
stant" which, in turn, is dependent
upon the kind of material used for
the dialectric. The idea Of a con-
denser Is to allow passage Of a ca.
pacity current and not to provide the
sort Of a conducting path as you
would have, for example, with a cop.
per wire. Whatever conduction is
offered by the arrangement of the
plates tt ar construction or the ma
terial used for the dielectric has to be
considered as leakage or loss.
Dielectric Absorption.
There is another form Of loss known
as "dielectric absorption" This is
the characteristic some dielectrics
have OF absorbing and turning into
heat some additional voltage after the
first charge. Of voltage is applied to
the condenser. | didn't burden Smith
with all the details Of this imperfec-
ton of the condenser but mentioned
it to him as just another sample OF
the popularity Of the condenser