Early battery-powered valve sets were based on valves such as the ubiquitous 201, which had a filament requirement of 1A at 5V. By contrast, some of later "battery type" valves required just 25mA at 1.4V to heat them.

In addition, the HT (high-tension) voltage required by the early valves used in battery sets varied from 60V up to about 180V, with valves such as the 1L5G being rated at 180V maximum. In practice though, the 1L5G was usually run with 135V on the plate.

This view shows the fully-restored receiver. It turned out to be quite a reason-able performer, especially after it had been aligned correctly.

The later "battery-type" valves operated at much lower voltages. They were generally rated at 90V on the plate but were often run at 67.5V.

However, there were valves that operated with even less voltage and current on the filaments, such as hearing-aid valves. In fact, the latter typically ran with about 22.5V on the valve plates. It’s also worth noting that the space charge tetrodes developed in the 1920s and 1960s ran with plate voltages from around 2V to about 20V.

We didn’t see many very low-current valves in Australia and the most common valve line-up in a battery receiver at the end of the valve era was as follows: 1T4 radio frequency (RF) amplifier, 1R5 frequency converter, 1T4 intermediate frequency (IF) amplifier, 1S5 detector and first audio stage and 3V4 audio output stage.

These valves all drew 50mA of filament current at 1.4V, with the exception of the 3V4 which drew either 100mA at 1.4V or 50mA at 2.8V, depending on how the filament was wired. The high voltage (HT) was usually 90V DC.