The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1925-10-23

condenSers and other instruments are
fastened are 81" sections cut from old
storage-battery containers. These con-
tanners are Of hard rubber. and make
excellent panel material. Cut them
with an old wood saw, the coarse teeth
make better-looking job than If a
hacksaw is used. In finishing, the
edges should be squared with q file.
and the sides smoothed with fine sand
paper, finally polishing with oil.
The wiring diagram shows the three
tubes used in parallel, so that they are
run from a single six-ohm rheostat.
This set uses the regular flve-volt
(storage battery tubes. The type 200
detector is a very sensitive tube. and
the 201A amplifiers are among the
best on the market at present. Clarity
Is secured by using only As volts on
the radio amplifier, and the loud
speaker power is obtained by loading
the audio tube to it's full capacity-as
much as 100 volts of "B" battery may
safely be used with a corresponding
"C' battery Of proper size; for 120
volts Of "B" use a 41k-volt &C" bat
terry.
To Add Fourth Tube.
AS already mentioned, this set was
designed mainly for clarity on all sta
tons using headphones. If loud-speak-
er volume is wanted for all stations,
another audio amplifier can be added.
Tho fro oh Il
ratio than the one suggested for the
first audio stage-a four to one is a
good ratio for the second audio ampli-
fer. By the addition of this audio
ampliffer loud speaker operation
should be possible at all times The
separate working of all tubes tends to
make it easier to operate than a re-
f1eXed four-tube set.
No provision was made on the board
for meter, but the use of either a
voltmeter or ammeter Is strongly rec
commended. The detector tube is es-
pecially critical, and it will be most
sensitive when five volts are supplied
to it. If 200-tube is used as sug-
gested, experiment with the "B" bat
terry voltage; sometimes lower value
may be better than 221s. The writer
had one new 200-tube that became
paralyzed with any voltage over IS,
and worked best at 1914 volts After
this tube had been in use for several
months the gas content changed, and
an increased output of satisfactory
quality could be obtained by using
1919 volts. To be sure the correct "B'
detector voltage is being used, tune in
on some station and try several "B"
values on that one station-retuning
If necessary each time a change Is
made-and use the "B" voltage that
seems best.
Winding the Coils.
Four of the FIVE coils are wound in
the well-known basket type, around
IL spikes set evenly spaced on 3A-
inch circle. Two coils of 60 turns used
with low loss 0O035 mid. condensers
form the two main tuning units. An
untuned antenna circuit coil of 80
turns is wound In the same fashion.
and plate coil of 20 turns feeds the
radio energy into the detector tube cir
cult. If long antenna is used. 1t may
prove advisable to use an antenna coil
of Is turns. A complete list Of coils
and cOndensers. lettered the same as
the wiring diagram. together with
other apparatus, is given below:
Coil and circuit Turns, wire, windg
Ii Antenna 80 20 DISC Basket
LIZ Radio ampl. grid 60 20 DISC Basket
L3 Detector grid so 20 DISC Basket
LA Radio ampl. plate 90 20 DISC Basket
LIS Ticker ;. 40 80 DISC 2k"tb.
Condens'r & circuit. Kind & ca acity
CT Rad. ampl, ting Cardwell .000S5 mfd
CO Detector /tun'g Cardwell .00O35 mfd.
CO Grid Mica fixed .00025 MID
CA Bypass Mica fixed .000l MID
Other Apparatus
Audio transf. 6:1 ratio Gen radio
Grid leak rs megohms
Rheostat ohms
Sockets Porcelain Hwy. springs