VRW  PUBLICATIONS          HOME   |   BOOKS  |   SERVICE DATA   |   RESTORATION   |   RADIO HISTORY

 

MAKES OF SET: PORTABLES    MAKES OF SET  BUSH  LISSEN  PORTABLES  AERODYNE  EKCO

 

Battery 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 LT radios.

 

These are your options:

  • Build 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).

  • For 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.

  • Build or purchase a power supply designed for the purpose.

  • obtain a commercially made 'battery eliminator' like the Amplion 'Convette' pictured here (only for all-dry type valves - basically, post WWII receivers).

SAFETY

Remember 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.

 

Safety 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.

 

SAFETY POINTS

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.

One effective way to prevent inadvertent shock is to make access to the innards more difficult - perhaps by fitting extras back screws.

Ensure 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 soldering iron.

 

ALIGNMENT

Portable 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.  

 

A 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.  

 

Where 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 affected.

 

 

GENERAL TIPS

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 type.

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 receiver.

 

 

Ever-Ready Sky Queen      

EVER READY 'SKY QUEEN'

 

Battery eliminators were popular for rable-model battery sets. This saved the regular expense of battery purchase

AMPLION 'CONVETTE' ELIMINATOR

 

Signal generators produce radio-frequency signals to assist in the alignment of IF transformers and RF stages (tuning stages). Correct alignment means highest gain, most sensitivity and can be critical to a set's performance

AN ADVANCE SIGNAL GENERATOR

VINTAGE RADIO world: SIXTEEN YEARS OF WEB PRESENCE