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VINTAGE RADIO
By JOHN HILL
Power supplies for battery receivers
Early radio receivers up until approximately
1927 were battery-operated with very few
exceptions. They used a variety of different
batteries, including dry & wet cells and
rechargeable & non-rechargeable types.
The late 1920s saw a market trend
away from battery-operated receivers
to "all electric" models that used
household power. These electric radios were much cheaper to run and
allowed many people to own a receiver in circumstances where they
previously may not have been able to
afford the high cost of battery operation. However, not all households had
electric power and battery radios were
manufactured until the end of the
valve era, even if they mainly took the
form of portables in those latter years.
I live in country Victoria and it is
surprising the number of old battery
sets that are still around. Perhaps one
in every six pre-1 950 receivers I find
is a battery model. Most of these sets
haven't been used for 30 years or more
and have often been stored in a shed
or a farmer's barn.
Personally, battery receivers don't
interest me greatly and their general
level of performance is only fair when
compared to mains-operated sets. A
battery output valve such as a 1D4 is
rated at 0.35 watts. When compared
to the 4.5 watts of a 6V6, the advantages of mains operation are fairly
obvious .
Despite my lack of enthusiasm for
battery radios , there are several in my
collection and there is a GE vibrator
model in the shed awaiting restoration. I'm not so one-eyed that I pretend that battery sets don't exist!
The main problem with batterypowered receivers today is the lack of
suitable batteries, for it has been many
years since they were made. Even if
they were still available, the price
would be prohibitive.
The battery eliminator
Back in the 1920s, there was a handy
radio accessory called a "B" battery
eliminator. Even today, an eliminator
is a handy thing to have if one is into
battery receivers.
There were several different types
of battery eliminators. Some were "B"
eliminators only, while others also
produced "C" battery voltages. More
recent types produced "A" voltages
as well.
A breakdown of these "A" , "B" and
"C" batteries may be helpful for readers unfamiliar with battery receivers.
The "A" battery's function is to supply the low tension current to the
valve filaments. Typical battery valve
filament voltages range from 1.5V to
6V.
The author's home-built 1A regulated power supply and the accompanying
small "B" battery eliminator will power most battery receivers.
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SILICON CHIP
The "B" battery supplies the receiver's high tension current and is
applied to the plates and screen grids
of the valves. "B" batteries were usually made in 45-volt units (sometimes
with a 22,5V tapping) and were used
singularly or in twos or threes , depending on the specifications of the
recei~er. Three large "B" batteries producing 135 volts was a fairly common
high tension requirement for many
battery receivers.
Finally, the "C" battery supplies the
negative bias to the control grids of
the valves. There is virtually no load
on a "C" battery - it only supplies a
negative potential to the control grids.
"C" batteries were usually either 4.5V
A "B" battery eliminator solves most of the problems
of operating old battery radios. Shown at left is an
Emmco eliminator of1927 vintage while immediately
above is a close-up view of the controls. This unit has
three outlets, two of which are variable. Some
eliminators also had a range of "C" battery voltages.
or 9V types with tappings.
An old original
ยท One of my battery sets is a 1938
model which still had its "C" battery
installed in a special battery holder
when I bought it. The interesting aspect of this battery (possibly the original) is that it is still in use today.
Unfortunately, the old "C" battery
was not dated but it is old enough for
the cells to be sealed with sealing
wax, which suggests that it has been
around for quite a while. The design
of the Eveready trade mark it carries
is similar to those shown in mid-1930s
radio books.
When checked with a voltmeter,
the old 4.5V battery measures 4.44V
but when short-circuited, it is so weak
that it cannot even manage a lmA
discharge. However, as the "C" battery's only function is to give the control grids a negative potential, this
ancient battery still performs its task
quite .well.
How one gets side-tracked; let's get
back to battery eliminators.
A simple "B" battery eliminator will
solve the most serious problem of operating battery radios. Finding 135
volts DC is difficult if one thinks only
in battery terms. If a "B" battery eliminator cannot be found, a home-made
version can be built using a suitable
transformer and a rectifier (either
valve or solid state power diodes).
Add suitable filtering and the appro-
This home-made power supply is used with a small 2-valve headphone receiver.
The "A" battery consists of two "D" cells, while the 90V "B" battery consists of
ten 9V transistor batteries.
priate high-voltage electrolytics and
bingo, you have a "B" battery eliminator.
If you are repairing an old "B" eliminator, the capacitors will most likely
need replacing to restore it to full
working order.
"A" batteries are not much of a
problem to substitute. Dry cells or
rechargeable nicads are OK for receivers with 1.5V or ZV valves. A
wirewound rheostat in the circuit will
help to control the voltage.
The old triode valves from the 1920s
with their 4V and 6V filaments need a
higher supply voltage. A small 6V
motorcycle battery will do the job
nicely and a suitable rheostat (about
Z0Q) will knock back the voltage for
use with 4V valves.
A rechargeable 6V motorcycle battery is also a good power supply for
any battery radio with a vibrator unit.
Most vibrator radios operated from a
single 6V supply rail, although some
required a 4V or 32V rail. Typically, a
small lead-acid battery will keep a
vibrator set operating for three or four
hours.
Low-tension receiver voltages can
also be supplied by regulated power
supplies. A regulated power supply
produces a virtually ripple-free current which is most desirable for battery valve filaments. A poorly filtered
DC filament supply can cause considerable hum in the loudspeaker.
A regulated power supply can also
be used as a "B" battery eliminator if
it is capable of producing sufficient
voltage. A simple 1-valve regenerative receiver often works quite well
DECEMBER1991
33
Rechargeable "B" batteries were not all that popular as they were messy, smelly
and expensive to buy. The unit shown here has 12 cells and is rated at 24V.
(Photo courtesy Orpheus Radio Museum, Ballarat).
on 30V, which is well within the capabilities of many power supplies.
Other options
There are also other power alternatives for battery receivers.
Last month's Vintage Radio dealt
with the building of a 2-valve regenerative receiver. This particular receiver is typical of the simple homebuilt radios that so many of us oldies
built in our youth. Like the receivers
in this month's story, the 2-valve
regenerative receiver is also battery
operated.
This particular radio uses two size
"D" dry cells connected in series to
light the filaments. A rheostat reduces
the supply to 2V.
The "B" battery is formed by using
five 9V transistor batteries connected
in series. These little batteries can be
This 1938 AWA receiver is a 4-valve battery set which
performs quite well. Many battery sets are worth
collecting and they are much more interesting if they are
in working order.
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SILICON CHIP
joined using their own snap connectors, soldered together or mounted in
a special battery pack as shown in
one of the photographs.
Although this "B" battery is quite
small compared to the large 45V batteries of yesteryear, its capacity is more
than adequate for the task. The little
two-valver draws just one milliamp
of high-tension current when the receiver is operating. This rate of consumption is only a fraction of what
the battery would be subjected to if it
were used in its intended role in a
transistor radio.
The 90V "B" battery shown in another of the photographs has had quite
a bit of use and most of the batteries in
it are six years old. Only two have
been replaced in that time. Despite
the battery's age, it still delivers irt
excess of 80 volts under load.
Dry cell shelf-life is very good these
days. Modern batteries are sealed very
well and the electrolyte does not dry
out. What's more, the purity of the
zinc used in their manufacture is also
better than in the past. This reduces
the amount of "local action" which
slowly destroys the cell from within. I
have an 11-year old "Sharp" AA cell
that still tests OK under load.
Rechargeable batteries
In bygone days, when battery-operated receivers were the norm, re-
This old Diamond 45V "B" battery came with a 22.5V tap.
Three of these batteries were used in the AWA receiver
shown at left to give a 135V high tension supply. (Photo
courtesy Orpheus Radio Museum, Ballarat).
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Despite being many decades old, this 4.5V "C" battery still delivers close to its
rated voltage. "C" batteries were used for grid bias in early battery sets.
chargeable lead-acid "A" batteries
were quite popular. These batteries
required charging at regular intervals.
If the household didn't have mains
power, then the rechargeable battery
had to be taken to the local garage or
radio service centre for its weekly or
fortnightly charge.
Less common was the rechargeable
"B" battery and this item, with a
charger, would probably have cost as
much as the average receiver did in
the 1920s.
My father built a rechargeable "B"
battery back in the 1920s. It was
charged direct from the DC mains using a globe in series with it to control
the charge rate.
Rechargeable batteries were large,
heavy, seepy, smelly things and a good
many users must have been very
pleased to trade them in on a mainsoperated receiver.
The Air Cell
One "A" battery worthy of mention
was the "Air Cell", and battery receivers from the 1930s era were often powered with this unique device. This
cell used a carbon/zinc element combination, with an electrolyte of caustic soda (sodium hydroxide, NaOH)
in water. It developed 1.4V on no
load, dropping to between 1.2V and
1.3V under typical loads.
A battery consisted of two cells and ,
as purchased, the cells were sealed
and contained the dry caustic soda.
The battery was activated by breaking
the seals and adding water. The name
Parts are available for the enthusiasts
including over 900 valve types, high voltage
capacitors, transformers, dial glasses,
knobs, grille cloth etc.
Circuit diagrams for most Australian makes
and models.
Send SAE for our catalogue.
WANTED - Valves, Radios, etc.
purchased for CASH
Call in to our Showroom at:
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A 45 volt "B" battery can be made
simply by connecting five 9V batteries
in series as shown here. Such a
battery has quite a long service life
when used with a 1 or 2-valve
receiver.
"Air Cell" was given to this unusual
device because it used oxygen from
the atmosphere as a depolarising agent
for the positive electrode.
When used with a 2V filament
string, a small amount of resistance
ranging from 0.6-1. H1 was needed for
typical current drains.
A single Air Cell battery could operate a 7-valve receiver (filament consumption 550mA) for 1100 hours. By
contrast, 36 No.6 dry cells at twice the
cost were required to operate the radio for a similar period.
In spite of this , the Air Cell wasn't
around for very long and this was due
to a number of factors. One was the
high initial outlay which many people simply could not manage, even
though it was cheaper to operate in
the long run.
It also had to compete with the 2V
accumulator which, even if less convenient, was more economical for
many people.
Another factor was the timing of its
appearance. Battery valve design was
evolving rapidly, particularly in the
area of operating economy, and eventually lead to the 1.4V-type valves ,
which were designed specifically for
dry cell operation.
At the same time, the vibrator-type
receiver, powered by a single large 6V
accumulator, was gaining popularity
as the supposed answer to the whole
battery problem.
But regardless of the type of batteries used, battery receivers were costly
to run and the power supply took up a
considerable amount of space. Many
early radios had quite sizable compartments in them to house batteries,
while others were built on doublestorey trolleys , with the lower shelf
used entirely as a battery storage area.
The mains-operated electric models
must have had great appeal when they
appeared.
SC
DECEMBER 1991
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