Conversion to AC/DC Universal Operation
THE PROBLEM
The introduction
by Act of Parliament of a National Grid System ot electricity
distribution in this country means that eventually all mains supplies
will be A.C.
(Alternating Current). In the meantime, whilst some supplies are still
D.C. (Direct Current) and in indefinite expectation of being changed
over to A.C., the buyer, possessor and maker of an electrically
operated receiver is faced with a very great difficulty. The same
problem has to be faced by the large number of people who lor one
reason or another change their place of residence.
THE SOLUTION
TUNGSRAM at
considerable expense and after extensive researches at their
world-famous Radio Laboratories have come to the rescue with a
wonderful
range of UNIVERSAL. VALVES—-valves that will operate equally well on
A.C. and D.C. mains. That disturbing hum which is usually associated
with an all-mains receiver is practically eliminated and the valves are
extremely economical in use—the consumption being only 35 watts.
THE METHOD
TUNGSRAM
UNIVERSAL VALVES are so constructed that they all require
only 0.18 ampere for the heater, as against 4 Volts at l.0 ampere for
ordinary A.C. Valves. The heaters are connected in series so that the
total current passing through is 0.18 ampere.
The resistance in the filament circuit consists of the following
sections :—
From tapping 260 volts to 240 volts -
120 Ohms.
From tapping 240 volts to 220 volts -
120 Ohms.
From tapping 220 volts to 200 volts -
120 Ohms.
In order to obtain the value of the main part of the resistance :
—
Subtract from 200 the sum of the valve healer voltages, then multiply
by 6. Thus, for instance, if the valve heater voltages added together
total 110, then : Main portion of resistance = (200 - 110) x 6 = 240
ohms.
On the diagram a further small section of resistance is shown, value 60
ohms, which is intended as a shunt for the dial lamps so that should a
dial lamp fail the receiving set will still continue to operate.
THE CIRCUIT
The circuit shown
in Fig. 1 indicates the basic system of wiring the filaments and
provided this system is adhered to no difficulty or trouble should be
experienced
Any modern Receiver can be constructed to take UNIVERSAL. VALVES.
Circuits described in the various wireless journals lor A.C. receivers
can quite easily he adapted for UNIVERSAL operation. In constructing
such a set it is only necessary to introduce the circuit alterations
described below.
THE CONVERSION OF EXISTING RECEIVERS TO
UNIVERSAL OPERATION.
1. If your present
set is designed to operate from a D.C. supply and you desire to bring
it up-to-date so that it will operate equally well from either D.C. or
A.C. mains, the only alteration necessary is to dispense with the mains
resistance now in your set and substitute another tapped resistance of
the appropriate size, the value of which is shown in the diagram Then
re-wire the rectifying circuit in accordance with Fig. 1 — an extremely
simple operation presenting no difficulties. Having inserted the
correct TUNGSRAM UNIVERSAL VALVES the set will continue to function
from your present D.C. mains and when your supply is changed to A.C. or
should you move to another district where A.C. is already the normal
source of supply, your set will require no adjustment whatever, with
the exception of the adjustment of the tappings on the resistance to
your existing voltage.
2. If the receiver to be converted is
an A.C. set, your first step is to do away with the existing mains
transformer, and then to arrange the rectification and re-wire the
filaments in accordance with Fig. 1. Insert the correct TUNGSRAM VALVES
and you have an up-to-date UNIVERSAL Receiver. It's all so simple.
TUNGSRAM ELECTRIC LAMP WORKS (G.B.)
LTD., 72, OXFORD ST., LONDON. W.I