National NC109
Written by Bryce Ringwood   

The National NC109 is a single superhet receiver made from 1957 to 1960 covering the medium and short wave bands in four ranges. It has the following valves:6BA6(RF),6BE6(Mixer),6C4(Osc.),6BA6x2(IF),6BE6(BFO/Prod Det),6AL5(Det, NL),6AQ5(Audio),5Y3(Rect),0B2(Voltage Regulator). 

The set features a single crystal filter arranged to provide variable selectivity and is one of the set's nicest features. The phasing control provides a notch which removes annoying heterodyes ('whistles of interference'). There is a separate band spread dial for the amateur bands, but it can be used for fine tuning anywhere throughout its range. Construction is on a copper-plated chassis, which looks attractive. In common with many sets designed for the amateur market at the time, the set uses dial-cord drives for band-spread and main tuning. The set runs out of sensitivity and gain at the high end of its range, but is still capable of receiving long distance stations, given the right conditions.National NC109 

The radio worked well for a while after I had replaced the power supply filter capacitors. It suddenly began to work badly on the 1.5 to 4.5 MHz band. I quite quickly realised that the tuning coil in the mixer circuit had gone open circuit. Fortunately, the problem was a broken lead at one end of the winding. Since all the coils are wound on a single former, removal and rewinding would have been a nightmare. I used to think coils must be very reliable components, but my casebook is littered with examples of open circuit coils in IF transformers, RF stages and so on.  

The radio originally had a drop-through transformer intended for a 110 volt supply. This had been replaced with a 230 Volt upright type.



 
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