Evening star., 1924-06-21

which must be done before the dry
cell tubes can be substituted for the
larger tubes The first is to provide
for the difference in tube prong ar
rangement and size either by sub
stituting regular dry-cell tube sock
cts in place of the sockets you are
now using, or by buying adapterS,
which can be inserted in the sockets
and which. in turn, will serve as the
sockets for the dry-cell tubes. With
such an arrangement no change in
socket wiring is necessary. All you
have to do is to buy the adapters, in
sert them into the sockets as you
would a tube, and then insert the
tubes in the adapters.
The cost of the adapters is about
equal to the cost of new sockets SO
that little is to be gained in the mat
ter of cost by buying sockets in
stead of adapters. In point of eff
cheney the adapter method is not
quite as good as the use of the right
type of socket, but it has the great
advantages of making it possible to
use either type of tube without fuss
or bother. With this arrangement
you can use the dry-cell tubes when
you are using the set as portable
set and the storage battery tubes for
greater efficiency when a storage bat
terry is available.
The other point which must be
watched in substituting dry-cell tubes
resistance of the rheostats used.
Resistance Is Different.
The resistance requirements of
these dry-cen tubes are different than
those of the storage battery tubes
AS matter of fact, these tubes re-
quire. a 30-ohm rheostat as against
the 6-ohm rheostat required by the
storage battery tube.
There are now on the market rheo-
stats DESIGNED
they give a resistance value of from
almost zero resistance to 80 ohms
The rheostat has three resistance
windings connected in series so that
the slider in passing from the point
OF very high resistance to the point
of lowest resistance passes in turn
over each winding. When the slider
is in contact with the high resist
ance winding the resistance varia-
tion is from approximately 10 ohms
the intermediate winding the re-
sistance can be varied from ohms
to Is ohms, while when the slider is
on the low resistance winding the
resistance can be varied from prac-
tically zero to 6 ohms.
In the diagram a method is shown
for adapting a receiver using stand
ard 6-ohm rheostats suitable for
storage battery tubes so that it can
be used with the dry cell tubes which
iCQuhC q uiSh TcSiSCdHCe. instead
of removing the 6-ohm rheostats and
replacing them with 30-ohm rheo-
stats another rheostat is mounted on
the panel and placed in the negative
lead Of the A battery Gf the rheo-
stats in the receiver are in the posi-
tive lead this auxiliary rheostat
should also be placed in the positive
lead).
In the diagram RI, R2 and R3 rep
resent the rheostats already present
in the receiver. R4 represents the
auxiliary rheostat used to introduce
sufficient resistance in the circuit to
cut the voltage down to the proper
value required by the tubes. R4
should have a resistance Of at least
20 ohms, A standard 25 or 80 ohm
rheostat can be used.
Decreasing the Resistance.
In operation with dry cell tubes the
resistance of R4 should be decrease
to the point where good signal
strength is obtained. Do not cut
down the resistance any farther than
necessary, as that will cause the tube
filaments to be heated excessively and
will lessen their life. When dry cell
tubes are used RI, RI and Rs merely
act as vernier rheostats or as
switches to turn or the filaments Of
their respective tubes when those
tubes which they control are not re-
Quired.
When storage battery tubes are to
be used the resistance OF R4 can be
cut out entirely-that is, the slider
is removed as far as it will go toward
the right. thereby reducing the re-
siStAnce to a minimum
Another method which can be used
- l. Q ~ ~Yt- a 49, 10 - IL