It is this booklet where I noticed it was stated inside the cover it actually that the term "radiotrician" is registered to the NRI. No other company can use the term "radiotrician" it's a registered trademark of the no longer extant National Radio Institute. It's a good reason that the term never fell into general use.
This booklet covers resonance curves, amplifer stages, choke coils, tuned transformers, tube capacities, neutodyne circuits, grid supressors, cross-modulation, pentode circuits etc. It's one of the most technically hardcore texts in the series. Best of luck.
You can get all 19.7 MB if you