Worcester Democrat and the ledger-enterprise. (Pocomoke City, Md.) 1921-1953, 1926-11-27
The Complete Line Supply Device
crihAdl

0~~~'
The biggest difficulty to be over
come in obtaining "a" current from
the house a. c. lighting supply Is in
finding rectifier that will pass suf-
ficient current for the filaments and
yet make battery elimination, an eco
nomical proposition. In the course of
description Of an efficient "a" "B.'
''C' line supply device in the Radio
Broadcast Magazine, B. F. Roland
writes as follows: "a logical solution
20 the difficulties of "a" power filter
ing Is to connect the fllaments of the
radio tubes In series, thus reducing
the overall current consumption.
"The accompanying diagram shows
q unit which has been found entirely
satisfactory for use in conjunction
with a receiver employing 1919 type
tubes in series. Due to the fact that
the current consumed is small, the
filter choke coils are of reasonable
proportions. This device will supply
vOltages and currents as follows:
"a battery-60 milliamperes. 6 to
80 volts.
"'B' battery-Up to 25 milliamperes,
at 200 volts. 80 (variable) volts. 45
(variable) volts.
&c battery-From 0 to 30 volts.
1.-THE use Of the device is, Of course,
restricted to radio receivers employ
ing tubes similar In characteristics to
the UX-199 or Dv-3 tubes with fla
ments wired in series. and under these
conditions its performance as uni
versal power Is ideal. The device H.
Illustrated is adaptable to any type of
radio circuit and has been used with
success on q three-circuit regenerative
set, the Browning Drake, and tuned
radio-frequency receivers, with varia-
lions of each type. Transformers
sistance or impedance-coupled ampli-
fers have been employed indiscrimi-
nately with equally good results.
The Power Transformer
I'm the diagram, T, is General ra-
dio power transformer designed for
80 watts, 40 volts, at full load. The
high voltage secondary provides $50
volts each side of the tap at the CEN
ter at no load. The third winding, t.,
provides volts at 5 amperes for the
raw a.. c. filament supply Of an UX-
112 or UX-171 power-amplifier tube.
This may be supplied by separate
flament lighting transformer. In this
construction, Brach unit serves the
purpose nicely. Across each half of
the secondary, T, Is connected OIL
microfarad buffer condenser, C, and ca
of 1,OOO-volt flash test type. The out
er ends Of this winding are connected
to the filament terminals Of standard
UX type socket, into which is plugged
the new type BIZ Raytheon rectifier,
Ra, which is capable Of passing So mil
lamps. The plate terminal Of the
socket, corresponding to the cathode
of the Raytheon tube, Is connected to
the plus side Of the filter circuit. The
filter circuit Of this power unit in
cludes choke coils, L, capable of pass
ing IS milliamperes direct current
without heating, and having a residual
inductance of at least % henries per
choke at this value Of direct current
The General Radio type 1865 standard
"B"-substitute choke is admirably
suited for this service. Others which
fulfill the above requirements will
probably be equally as satisfactory.
"The voltage-control unit shown at
the right-hand end of the diagram
has been tried under all conditions
and has given good service. There
was some difficulty in obtaining prop
er values and current-carrying capaci.
ties of the various resistOrs and, after
considerable testing, the units speci'
fed were adopted. All of the parts In
the control unit may be obtained from
regular stock Of the various manufac
turers or their dealers. For the plate
voltage Of the power-amplifier tube
the maximum 'B' plus is taken direct
ly from the terminals of the filter cir
cult. This terminal provides approx
mately 200 volts at full load, A claro
stat, r., is used to control the volt
age output Of the next lower tap ('B
plus Int.) and will give from 80 tC
135 volts approximately on the usual
plate-current drain. at this voltage
The 'B'-plus detector tap Is obtained
through the use of another clarOstat
or a Bradleyohm No. 10. r. One-mi
crofarad condensers are connected in
both Of these cases from the b plus
variable to 'B' minus to bypass rheo
stat noises, and to prevent undesirable
coupling between the various ampli
fer stages.
&C" Battery Voltage.
"The &C. battery voltage is obtained
from wire-wound variable resistance
of the proper value. AS this resist
ance carries the full-load current Of
the device. II must be designed tt