Dominion Battery Screen Grid 3

Despite its slightly home-made look, this is a commercially manufactured receiver from 1928. The right hand dial is used for tuning a station and that on the left for peaking up its strength. The two dials needed to be kept roughly in step in order to hear weaker stations. The upper centre switch is for selecting the long or medium waveband (the latter referred to in 1928 as the short waveband) and the lower switch for turning the set on and off. Because of the simplicity of design and the valve characteristics the on/off switch merely interrupted the filament current to the three valves. At the side of the set was the reaction control which would double as a volume control. This model required a high impedance external loudspeaker.

As you can see it's made by The Brownie Wireless Company of London and the valve types are mentioned on the label. Useful information if the codes are not visible as is indeed the case here. The leftmost valve has no markings visible and is slightly unusual in having a B4 base with a side connector. Usually this side connector was fitted when a B5 base left no room for a 6th connection. The valve is an Osram PT230 which is not a very common type. It's said to be a pentode, but this will have to wired with its supressor grid connected to its filament and the screen grid to the side connector. The centre valve is as the label tells us a 210HF but the RF amplifier, originally a 210SG is now a Cossor 215SG tetrode which is pretty similar but has the advantage of consuming 150mA filament current, 30mA less than the original.

For some odd reason the makers decided to fit a rather odd shaped back to the set. The chassis is also a peculiar shape, perhaps made to allow an accumulator to be positioned in the space? The battery lead however implies by its length that the HT, Grid-Bias and accumulator were positioned some distance away. A wooden panel is fitted behind the valves so you can't see the tuning condensers. A useful addition to this model is provision for connecting a gramophone. Although most in those distant days would be acoustic types, people able to afford commercially produced receivers should be able to afford an electric gramphone.

Here's a close-up of the small section of chassis where the tuning coil is located. Attached to the right side is the solid dielectric condenser reaction control.

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