portable valve radios were very common throughout the valve era. In fact, at the
start, batteries were the only possible power supply - valves with 'heaters' for
AC mains working came after battery (DC) types.
Because there was a very large market for
portables, lots of them are still available. Many sets,
especially the later 'all-dry' miniature valve designs, are potentially simple
restorations. They often lack the complexity of mains-powered radios and because
of the limitations of battery power, rarely ran 'hot' or, due to the high cost
of batteries, for
long periods at a time. Time may have compromised the capacitors, and one
or two resistors may have risen in value, so ideally, checks should be made
before powering up.
Some points made
on these pages apply to these
later, B7G based all-glass miniature-valved sets, although much is common to the earlier wet-cell 2V
are your options:
an HT battery by stringing together a series of ten 9-V batteries end to end
(for 90 volts ht) or thirteen 9-V batteries (to supply about 120V HT, suitable
for the older sets that use 2-V accumulators for LT).
LT requirements, all-dry sets need only a normal 1.5V cell to power the
filaments, although their quite high current requirements will be better met
by wiring two or three single cells IN PARALLEL (NEVER SERIES). This will
increase the life of the LT supply. With 2V valves, a 'CYCLON' sealed lead-acid battery, obtainable
from Farnells, could be used to replace a missing accumulator. Probably the
best course would be to purchase a single 2.5AH or 4.5AH cell and solder
connectors to its tags. Some form of charger would be needed to keep the
cell topped up.
or purchase a power supply designed for the purpose.
a commercially made 'battery eliminator' like the Amplion 'Convette'
pictured here (only for all-dry type valves - basically, post WWII
that battery-only radio sets were never designed with mains powered operation in
mind. For example, control knobs will probably be held by exposed grub screws.
Obviously, there's little danger of a fatal electric shock from a high-tension
battery* but it is a different story if a badly designed mains unit is fitted to
convert the set. Great care should be taken when making power supply units and
precautions should be taken when handling a set converted by someone else - at
least until you've checked things out and are satisfied that things are as they
should be. Remember too that vintage eliminators may not be safe and should be
checked before use for insulation by a qualified person.
Which should not be taken to mean the HT batteries are perfectly safe.
They are not, if mistreated and even if a shock isn't fatal, it is an
unpleasant experience. Also, shorting such high potentials can cause
excessive heating which can lead to fire.
precautions are not simply for the sake of the radio enthusiast, but also for
anyone who may come in contact with the set when in use: children, partners,
relatives, subsequent purchasers.
Obviously, a battery-only receiver does not,
under normal circumstances, pose a problem of electrical safety to the user.
Batteries have far too high an internal resistance to allow lethal currents to
be developed. It follows that makers tended to disregard safety aspects. For
example, access to the interior of such sets, far from being made consciously
fiddly, is often very simple and quick – essential when changing batteries.
Knobs are usually attached with grub screws. Cabinets may have metal external
parts which are not internally earthed, such as speaker grille.
None of these points make battery sets dangerous
when used as the makers intended. It is only when such sets are coupled in some
way to the mains supply, perhaps by fitting some kind of power supply,
that safety has to be considered. Providing that any mains or high
voltage points are well insulated and cannot come into contact with fingers,
there should be no real problem.
It is essential that any
mains-driven power supply should
use a fully isolated double wound transformer, properly earthed.
effective way to prevent inadvertent shock is to make access to the innards more
difficult - perhaps by fitting extras back screws.
knobs are well seated with no exposed metal control spindle accessible. Grub
screw holes can be sealed with melted wax crayon of a suitable colour, using a
valve equipment must be set up with accuracy if good results are to be obtained.
There is little room for error. If there is no sign of IF transformers or
trimming capacitors having been tampered with, they are best left well alone
until such time as testing points firmly to faulty alignment of either the IFTs,
the RF stages or perhaps both.
reliable and accurate signal generator is essential for accurate alignment. A
multi-test meter can be used as an output meter, but do not rely upon your ears
to tell you when maximum output is achieved, because the human ear cannot
accurately distinguish between quite widely varying levels of sound.
receivers are normally operated from internal frame aerials re-alignment must be
carried out with these aerials in circuit. For R.F. alignment the signal should
preferably be injected via a standard shielded coil.
The connecting leads should
also be screened. For preliminary adjustments, it may
prove necessary to loosely couple the signal-generator output lead to the
grid of the frequency changer valve by laying the lead near to this point. The
receiver should always be aligned with the batteries and loudspeaker in the same
position relative to the frame aerial as would be the case under normal
operating conditions, otherwise the inductance of the frame aerial may be
Many restorers recycle spares from scrap radios
to restorable mains powered ones. Purchasing a battery radio for this purpose
can prove to be a problem, for the following reasons:
Battery sets generally use capacitors of a
lower working voltage rating than mains-powered sets require.
Resistors found in battery sets are always of
a modest current rating: values of a quarter-watt and less are common.
Again, these may be unsuitable for use in the higher powered mains set.
Output transformers are of a lighter
construction and are made neither to match nor withstand the power
requirements of a
mains output valve.
Loudspeakers, on the other hand, tend to be
very sensitive types and these may well prove useful at times, providing the
mains set is of a modest power rating, for example a TRF or small table
Of course, all such components are in general
suitable for restoring other battery-driven radios, though it is my belief
that capacitors are better replaced with new or new, old stock (NOS) types
as the reliability of old capacitors is often suspect. Electrolytic
capacitors are usually best replaced by new ones unless you can reform them.
Battery portables were designed for
sensitivity and low running costs, not for hi-fi reproduction, so do not
expect the reproduction to be of the quality of a good mains powered