17—16.
D. C. AMPLIFIERS
409
Seller11 has replaced the batteries of gure 17—24 by two
batteries and a series of resistors, as in gure 17—25. By
choice of the resistances,it is pOssible not only to supply the
.
proper voltages to the tube, but also to make the balance much
more stable; i.e., free from,
small voltage changes of the :
_
l
battery, etc.
l
'
@
_
@
5.3 l
Various improvementsof l
_
"'5
Ï
a ;
the Soller circuit have been
!
‘
_
40
…
20
,8
i
made to secure greater sta;
«+
i
_
'
"
bility of balance, one of the l.
l‘…—___)
_Ë
best of which is shown 12
in gure 17—26, where the
Fm. 17—25.
The Seller circuit.
'
‘
space-charge-grid currents
are used to assist in overcoming battery and emission changes.
"
Currents of the order of 10”14 can be_measured With c0mparative ease With these tube circuits. By enclosing the tube
and that most critical portion of all tube circuits, the gridlead, in
an evacuated chamber, it has been‘possible
13 to measure currents‘
of the order of 10‘17 amperes,
such as supplied by the ionization
__________
due to a proton in a shallow -
.
50; chamber. By way
Of Com—
5.
E "_parison
With a Ho"manr‘r
i
7
"
.
‘
4000
2000
! duant electrometerof
sen31—
i
_
'°"°
! tivity 20,000 m11hmeters
_:
:
per
Volt and a period of 30
;
50
5‘
i seconds, the tube circuit had
:
_
lillm
sensitivity of 250,000
_'millimetcrs per
VOlt and &
È‘IG. 17—26. A stable d.c. amplier.
P€Ï,i0d (Of the galvanom—
‘
,
,
eter) of 5 seconds.
,
-
The electrometer triode of Philips COHSÏSÎS.Qf tW°
one the grid, the other the plate mounted parallelto .e?Ch
other _m
the tube.
The lament
between“and parallel
to
plates. Practically all of the
.
go to the plate. Poten‘tials
on
Sm-ajf'i
'
—
.
.in the plate current. The structl}re‘
at
input resistance .is suicientlÿrhlgh for ‘ use
,
curre
_
__
measurements.
-
'
'
.”
:
'
…
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