Belt Valley times. [volume] (Armington, Mont.) 1894-1977, 1926-12-30

hfOustu All over the CuuILFy Dy hEtll
Henney's articles on the Lab cir
cult which has been appearing II
Radio Broadcast Magazine. In a re
cept Issue Of the same publication
John Brennan, technical editor. de
scrIbes the construction Of such a re
ce4ver. which, although employing
only four tubes. is sufficiently sensi-
tive. and produces satisfactory vol
ume. for average requirements. Refer
ence to the accompanying diagram at
once brings 10 our mind at least one
unusual feature. We note that II reads
from right to left instead Of vice
versa. The reason that the apparatus
has been laid out for signal progress
sion from right TO left is that, by so
doing. connection between the coils,
sockets. and transformers. etc, are
made as short as possible. In some
Instances the connections between GER
tain apparatus In the original model
require no wire at all. the Tugs them
selves being long enough to meet and
be soldered together.
Wiring Behind Tube Sockets.
This novel form OF construction also
enabled practically all the "A" "B."
and "C'' wiring 10 be carried behind
the tube sockets and to be cabled
The cabling Insures against feed-back
between the various units comprising
the receiver. Mr.. Brennan's receiver
employs a panel shield When Rice
naturalization is employed. this shield
ing is very much to be recommended.
for. otherwise. hand capacity effeCts
would probably be noticed, and Il Is
naturally TO best advantage to elm
mate these as much as possible. Neu-
tralIzation by the Rice method is prac-
ticaliy Independent OF frequency. or,
said In another way. one adjustment
Of naturalization will be sufficient
whether the set is being tuned to the
long or short broadcastlng wave
lengths.
References to the diagram shows
that two r. T. choke coils are employed
in the tuner circuits. Both of these
are Samson IS millinery chokes.
They are shown in the diagram be-
tween the numbers 6 and Z, and q
and %. That In the secondary circuit
OF the antenna tuner Is useful In pre-
venting oscillation OF the circuit at
the extremely high frequencies OF
Ebout $3.50 kc. (about so metersl In
the detector plate circuit the choke is
employed to prevent r. T. currents
passing through the primary of the
audio transformer Across the sec
ondary of this first transformer is con-
nected a variable resistance unit OF
100000 Ohms maximum. This acts as
an efficient volume control.
In the output circuit are arranged /
an audio frequency output impedance
unit and large capacity condenser so
that the diaphragm of the loud speak
er may be operated free from the ex-
drag likely to be imposed upon
It by the d. c. component OF the high
''B" potential on the plate OF the final
tube. The Hadle lReedanee unit EN-,
ployed here is Samson tipped out
PIT col and due e tAe fact that the
mpedance OF this cOil }nay be approx.
lmately matched to the characteristics
Of the loud speaker on account Of the
tappings. better quality is possible.
The condenser employed at this point
has a capacity OF mfds, The fol-
lowing list OF parts Is recommended
In Radio broadcast:
List Of Parts.
Two Cardwell OO0035 mfd. con-
1ensers, type 169E.
Two Lab" circuit tuning coils. Gen.
win.
1wo Marco Illuminated dials
Four sockets. air gap.
Two American .audlo frequency
first and second stages.
One XII neutralizing condenser, type
Two Samson choke coils, IS MILF
lenries.
One Samson output impedance. type
One lobe Deutschmann bypass con-
lenser. mfd.
One Tobe Deutschmann output con-
Ienser. A MID.
One Electrad Royalty variable res.
meg.
One Electrad flament switch.
enc Elecsxad grid condenser. 0.0o0ea
ND.
one Electrad fused metallic grid
sak, A megohms.
Two Brachstata. u ampere and x
mpere.
Two Frost pin jacks
One Precise mIcrodenser. type 04O.
0 mmfd.
Nine ri. binding pests
One Radlon binding post strip.
One panel. BY q hy BIG inches.
'Ormtca.
One FFlkz cabinet
So that power tube may be used 4
D the last andio stage the iilamenf 4
firing TO this socket includes q sep q
rate Mampere ilameni ballast. such q