Sn direct dating
Many radio engineers of the thirties firmly believed that the absolute best sensitivity and stability of a communication receiver's RF amplifier, First Detector and Local Oscillator could only be achieved by using "plug-in" coils.This type of approach eliminated problems of lead length, shielding and stability along with isolation of unused tuned circuits - problems that were commonly found in broadcast receivers using conventional rotary bandswitches. Handling three individual coils for each band change, storage of the unused coils and how to remove B when changing coils all added to the counter-belief that plug-in coils were archaic.Another portion of the design involved the PW gear drive used on the NC-100 series.The famous HRO PW gear drive used a "precision worm" (PW) gear to drive a large split-gear with two ganged variable condensers flanking each side of the gearbox.The HRO wasn't hassle-free though and Millen realized that for the SWL (Short Wave Listener) and intermediate-level hams, in other words, those who didn't have the experience or couldn't afford the 0 HRO receiver, there had to be a design that would provide the excellent performance of plug-in coils without all of the hassles and expense.
A large band selector knob on the front panel of the receiver would turn a rack and pinion gear mechanism that would move the coil catacomb into place, thus engaging the proper coil set pins into short, fixed position, spring-contacts mounted under the tuning condenser in insulator blocks.
The split-contacts were not soldered together but rather had the screen voltage wires connected to each of the two halves of the contact and when the coil pin, which wasn't connected to anything inside the coil catacomb, engaged in the two halves the circuit is completed and the screen voltage was then routed to the RF and IF amplifiers.
To keep the costs down by keeping the physical size of the catacomb relatively small only three sets of coils were used per tuning range.
The phase diagram of the Yb–Sn system has been revised in the composition range 55–70 at.% Sn using differential thermal analysis, X-ray diffraction, optical and electronic microscopy.
Includes NC-100, NC-101X, NC-80X, NC-81X, NC-100A family, NC-200, NC-240CS, NC-240D Dept of Commerce & CAA Airway Communication Receivers Military Versions - RAO family, RBH, NC-100ASD, R-115, R-116 History of Design and Production, Moving Coil Catacomb Details, WWII Versions, Post-WWII Production, Serial Numbers, Restoration Write-ups Besides National's masterpiece, the HRO, another series of receivers produced by National Company, Inc.