The Ekco company were leaders in the manufacture of mains eliminators and battery chargers for radio sets
(click the valve to read more)
Model
AC12 with its case removed
Stamped on the chassis is the
Serial No 247149Ready for refurbishment is this Ekco Model AC12. Ekco made battery eliminators from 1925 and the booklet opposite dates from August 1931. In it are described seven models for AC mains and one model for DC mains. Written inside the back cover in my granfather's handwriting is the note that the guarantee expires in December 1933. He must have purchased his model in time for Christmas 1932. Other similar models were the AC18 and the AC25.
Specifications for two typical standard AC models available in 1931 are given below:-
120 volts up to 12mA or 9mA if the 80 volt 2mA or the SG 60-80 volt 1.5mA tappings are in use.
120 volts up to 18mA or 150 volts up to 13mA or 14mA and 9mA respectively if the other HT voltages are used
Adjustable 50 to 90 volts up to 3mA
Lower voltages obtained with base connector screw in position "L", when 100 volts at up to 14mA to 120 volts at 10mA depending on drain from other outputs.
There were a number of AC mains models which included battery chargers, two of which are described below..
As the AC12 but includes an accumulator trickle charging output
As you can see in the picture above, the design of the AC units is pretty basic, using a double wound mains transformer, an iron cored HT choke, a capacitor block and some resistors. Rectification was carried out by a small, finned, full wave metal rectifier. Voltage outputs were dependent on the amount of current being drawn. This is due to the relatively high resistance of the rectifier and the use of resistors to provide the lower voltage tappings.
This model is larger and heavier than the others depicted in the catalogue shown above and carries the label "Combined Unit" as like the K12 includes an accumulator charging facility or filament supply as well as an HT supply.
Underneath are tappings
for 200-225v and 225-250v mains at 40-100 cycles and also a setting
for 2, 4 or 6-volts. this would allow the unit to feed either
an accumulator or a set of indirectly heated valves. If directly
heated, battery type, valves were to be fed directly the level
of hum from the crudely rectified low voltage would be overpowering
but this rough low voltage DC supply would be perfectly good for
mains type valves, with their isolated heaters.
On the high tension front, numerous voltages are provided for screen grid valves and several tappings for different HT levels.
As DC mains were quite
common before WWII, Ekco included a DC model in their range. Because
of the vagaries of current and voltage (as explained in Ohms law)
there's a tapping under the unit for running at either 15 or 25mA
(The designation for milliamps loosely inscribed as "MA")
Tappings for screen grid and HT are provided, as the with the AC units, by sockets and a jumper on the centre panel.
This example has been refurbished by its last owner and finished in a matt black paint. Originally it would have had a shiny bronzed finish.
Also manufactured by Ekco was the TC1 accumulator trickle charger for 2, 4 and 6 volts
This
is the T500 accumulator charger, dating from around 1929
or maybe a little earlier and is the precursor of the later TC1
This early model is in the same range of products as the boxier looking models shown here
Safety-wise the newer units complied loosely with new IEE regulations in force in 1931. These called for a number of recommendations, for which the units only comply if the user follows the instructions in the booklet.
Earthing the case is done via a wire to a terminal provided on the underneath of the chassis. Most people would use two-wire mains cable, often connected to a light socket via an adaptor. An external earth wire would have to be carried from the receiver to a suitable earth connection.
There is no fuse included in the unit although the regulations called for two fuses, one in each side of the feed to the unit. Ekco got round this by advising the user that such fuses were to be found at their mains distribution board and if this wasn't the case then they were advised to fit a couple of 3-amp types.
Headphones and loudspeakers used on the radio being powered by a mains eliminator had to be connected through a double-wound transformer and customers were advised to procure one from their radio dealer. No doubt many users were surprised by tingling sensations as they adjusted their headphones.
I would imagine that in many cases none of the above recommendations would be followed. Nowadays the manufacturer has to ensure that his equipment is foolproof, leaving no latitude for the end user to ignore safety.
This old unit probably dates to the early 30's
and could charge an accumulator and also supply HT for a battery
operated radio.
It used a metal rectifier for HT rectification.
Interior view
Where's the HT rectifier and smoothing condensers?
Presumably long since defunct?
Top left is a bank of small coils, connected to the stud-switch, used to reduce the HT voltage.
see more old battery chargers