Plug-in coils to select the tuning ranges, a separate power supply and a micrometer-type tuning dial are foremost in the design and were to become standard features for National receivers over the next several years.Since the RHM was a commercial airways receiver it had to be built with the best material and best parts available to assure top reliability and performance.
National got the contract for the ground-based airport receivers. and his West Coast design team were involved in some of the electronic engineering work of the new receiver that was designated RHM.The RHM was National's first superhet and it had some of the features that were to become National's trade-mark.RCA supplied some airports with this 16 tube superheterodyne receiver beginning around 1937.The receiver used many of RCA's developments, including the "Magic Brain" which was a modular receiver "front end" and the innovative "band-in-use" dial mask.The RHQ was also identified as the AGU receiver in some uses.
Also, National produced a long wave receiver built along the same lines as these early airways receivers, the RIO.
It is all original and has its complete original coil set (15 coils) in the original rack mounted coil holder.
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.
Actually, the Comet Pro was only 5 (and it had a built-in power supply) but it didn't have an RF stage and required an external pre-selector for image-free reception above 10mc.
The Comet Pro came out in 1931 and, from 1932 up to about early 1934, only National and Hammarlund were offering commercially-built, shortwave superhets.
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 Hi-Z speaker solenoid coils connect between AF plate and B - just like an audio output transformer.) The RHM functions quite well with 75 year old components - every part was the best that was available at the time.