Farm Lighting Systems

Radio Record, Volume II, Issue 13, 12 October 1928, Page 26

Farm Lighting Systems

For Filament Supply

PANY country homes have their own electric light plant, generally of low voltage, ranging from 382 to 110 volts, and usually direct current. This latter fact makes it a rather easy matter to obtain filament current from the house mains, especially in cases where the lights are supplied from a bank of accumulators, and not direct from the generator. In whichever way the current is supplied, the two diagrams herewith show two alternative arrangements for cutting down the voltage of the supply for use on valve filaments, The essential factor is the correct resistance value used for the voltage

reduction, and this resistance is marked R in each of the diagrams. Its value in ohms is given in the accompanying table, and, besides being suited to the voltage of the house supply, varies with the number of valves employed, the six-volt type being provided for :-

In the above table the first column gives the number of valves in the receiver; the next two columns the resistance value of R in ohms and the watts passed by the resistance when on a 382-volt supply. The last two columns give the same particulars of resistance and watts fo a 110-volt supply. Using these figures as a guide,

and with a reliable voltmeter as a check, yoltages between 32 and 110 could be provided for. Where the supply is not from accumulators, the usual smoothing arrangements for direct current must be provided, consisting of suitable lowresistance chokes and high- capacity condensers. The Alternative Schemes. WO circuits are shown in the diagram, of which No. 1 is the easier to use, but in the case of working direct from the generator may possibly give a certain amount of hum that can be heard in the loud-speaker. That being the case, No. 2 circuit should be utilised. If No. 1 is used, a'20-ohm resistance is placed in series with the reducing resistance and the positive and negative terminals are connected to the respective terminals on the receiver. If No. 2 is used, the B negative and © positive leads are removed from where they connect on the receiver, and in-__--stead are connected to the centre point) of the 20-ohm resistance. When this arrangement is used a positive bias is produced by the connection of the "bove-mentioned B and C leads to the centre of the resistance, and to compensate for this the C voltage on each valve to which it is applied should be increased by 38 volts.

No. Valves 32 volts. R OL 35 at 21 18 15 13 12 Ww 15 22 30 BT 43 a0 at 66 110 ~olts. R W 190 oe 130 84 100) 105 80 135 65 160 58 190 50 = 210 4.55 240