National’s first radio products under Millen where the L3 two stage audio amplifier and E1 single stage audio amplifier with built-in battery eliminator. These were released in 1927.
Soon to follow in late 1927 was a 2 valve short wave receiver, the SW2. Based on a design obtained from RCA communications laboratories, it comprised a tuned rf amplifier and regenerative detector. It covered the frequency range 2.6MHz to 20MHz using four plug-in coils.
The SW2 Receiver

In 1929 National developed the SW2 into the SW4 by adding two stages of audio amplification. It cost $49-50 plus an extra $5-25 for the case.
The SW4 Receiver

Also in 1929 they started marketing Fred Drake and Glen Browning’s designed broadcast tuner the MB-29. This was a TRF set consisting of three stages of RF amplification. In 1930 they developed it into the MB-30 by adding an additional stage of RF amplification.
The MB-30 Receiver

In 1930 they also produced the SW-5 short wave regenerative receiver by replacing the single ended audio output stage of the SW-4 with a push-pull amplifier. The SW-5 was one of the first short wave receivers designed specifically for use from AC power.
The SW5 Receiver

With the onset of the great depression a cut down version of the SW-5 was produced. With just three valves the SW-3 became the receiver of choice for radio amateurs that could afford it and also saw use by commercial airlines. It remained in production from 1933 to 1948. It used nine plug-in coils to cover the 350kHz - 33MHz range.
The SW3 Receiver

The excellent performance of the SW-3, when compared with other receivers of its vintage, was in no small way due to National’s use of a new material for its coil formers called R39. In the 1920s, the moulding powder sold by the Bakelite Corporation was based on wood filer and was very hydroscopic. Added to this the traditional moulding process was done by steam and the moulding room was an extremely humid environment. The result was that formers manufactured by this process resulted in coils with unpredictable Q values. In 1930, the Boonton Rubber company started making coil former mouldings using ground mica in place of the wood filler and electrically heated presses. This provided the R39 formers used by National.