Dating the national hro
This particular set, the HRO-M, the M meaning that it is the military version is from the first year's production and it used tubes with 2 volt filaments.
In 1934, Millen envisioned producing a high end receiver targeted at radio amateurs.
His goal was to bring it to market by the holiday season in December of that year.
All of the consumer radios used TRF or regenerative topologies (Note 1).
Another prominent engineer, James Millen began work as National's Chief Engineer in 1924.
One can make the philosophical argument that war brings very little benefit to mankind. (1) They employed, or were associated with, pioneering engineers such as Fred Drake and Glenn Browning.
The National HRO, in one form or another, remained in production well into the 1970s, finally ending its run with a solid state version.
GE built the transmitters and asked the National Company to design and build the receivers.None the less, completing a prototype based on a radio not yet in production, in such short time, would be a challenge.The engineers nicknamed it the "HRO," which stood for "Hell of a Rush Order." The name stuck.The pace of technological advancement that would occur in World War II would be unsurpassed until the invention of the personal computer in the 1970s.Pictured above is a National HRO, a nine tube TRF/heterodyne hybrid.It could tune from 50 k Hz (far below the broadcast band) up to 30 MHz, which was considered the practical limit for short wave communication at the time.