Mechanical Engineer James Millen joined National as General Manager and Chief Engineer in 1928. Millen was a Stevens Institute graduate and an enthusiastic ham. So it was natural that he guided National into the ham/shortwave receiver market.
James Millen and the National engineers put considerable effort into the SW-3 design to achieve maximum performance in a three-tube regenerative receiver. In March 1933, Radio News published an article by James Millen titled "Testing a Modern Superhet" that described National's procedure for testing and aligning the AGS receiver. In the article there was a photo of the Radio News' AGS set-up that showed they were using a National Dog House power supply and a set of Hi-Z 'phones for the audio output. I've been running my RHM in this fashion also, using a National 5886 PS (6.3vac Filament and +180vdc B+) and then listening on a pair of Type-C Navy Baldwin 'phones. This has given me the best results, although if I don't want to use the "Baldies," I can connect up a Hi-Z magnetic cone speaker like a Radiola 100A which then eliminates the need for an audio output transformer and provides ample volume.
The RHM functions quite well with 75 year old components - every part was the best that was available at the time. Today, the RHM performance seems antiquated and crude but in 1932 it was "state-of -the-art" and the fact that the receiver is still operating and is still accurate in its dial readout is testament to National's build quality and Herbert Hoover Jr. and James Millen's design capabilities.
James Millen (at National) headed the mechanical design team and Herbert Hoover Jr. (on the West Coast) was in charge of the electrical design team. Millen and Hoover believed the best receiver performance was obtained using plug-in coils thus eliminating the losses found in most bandswitch circuits of the day. Millen believed that a lower noise figure was achieved using the 2.5vac tubes but later recanted this opinion as the 6.3vac tube quality improved.
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Some Millen Products
Millen 90501 Secondary Frequency Standard
Millen 90501 Secondary Frequency Standard (Rear View)
Millen 90671 SWR Bridge
Millen 90651 Grid Dip Meter
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Some Millen Products