September 1937 QST
articles are scanned and OCRed from old editions of the ARRL's QST magazine. Here is a list
of the QST articles I have already posted. All copyrights are hereby acknowledged.
The National Company
of Cambridge, Massachusetts, was one of the first large distributors of electronics components and appliances. Believe it
or not, National began life as the National Toy Company. Thanks to the efforts of
Mr. James Millen, W1HRX, in designing and marketing
high quality radio products, the company evolved into a favorite source by both amateur radio operators and casual listeners
of shortwave radios. The NC80X covered the commercial broadcast band and a couple shortwave bands, whereas the NC81X covered
only multiple shortwave bands for amateur radio use.
National Company Catalog & NC80X / NC81X Receiver Advertisement
As usual at
this time of year, a new National catalog is ready. Also, as usual, you will want a copy for it is free for the asking,
and easily the season's best bargain. You will find several noteworthy new products between its covers, among them the new
NC-80X and NC-81X. These two new receivers belong to the SW-3-FB-7 tradition, for they are thrifty, reliable, and capable.
Also they are a lot of fun to operate for reasons that will be evident when you get your hands on one. You will find a page
from the new catalog describing them on the other side of this sheet. There are other new products, too, such at the multiple
crystal holder; to say nothing of old products revamped, such as the receiving type sockets which have new conveniences
and adaptability. And of course, there are the old reliables like the R-100 choke and the TM condensers, which are as well
known as the trade-mark they carry.
Your dealer has a copy for you.
National High Frequency Receivers
NC80X and the NC81X
This is an inexpensive receiver having exceptional operating characteristics. Ten tubes are used in a high gain superheterodyne
circuit as follows: 1st detector 6L7; HF osc. electron coupled, 6J7; three IF stages, 6K7's; linear 2nd detector, 6C5; amplified
and delayed AVC, 6B8; panel controlled beat frequency oscillator, 6J7; beam power output, 25L6G; and rectifier, 25Z5. The
IF amplifier is of entirely new design, operating at a frequency of 1560
KC, and providing a high order of image suppression, better, in fact, than that
obtainable in many receivers having elaborate preselectors. The crystal filter (2nd IF stage) is truly remarkable in its
performance, since selectivity is continuously variable between 400 cycles for single signal CW, and 5 KC for high quality
broadcast. The range of the phasing circuit (heterodyne elimination) has been similarly extended. With such unusual characteristics,
the crystal filter remains in the circuit at all times, simplifying tuning considerably. With the development of the 25L6G
beam power tube having an undistorted output of 2 watts, it has become possible to design a high performance communication
receiver operating with full efficiency on either AC or DC, 115 volts.
The tuning system, likewise entirely new, employs a multiple scale dial of the full-vision type, accurately calibrated
in megacycles. Several unusual features are incorporated, such as the mirror for overcoming parallax, the auxiliary linear
scale (at the bottom), and the adjustable frequency markers, by means of which any particular stations, or frequencies,
such as band limits, may be "logged" on the dial itself. Two vernier reduction ratios are available, 16 and 80 to 1, with
a separate knob for each.
Automatic plug-in coils are used, controlled by a knob on the front panel, as in the NC-100. This arrangement has proven
itself to be thoroughly reliable and efficient. The frequency coverage is continuous, except for a small gap at 1560 kc.,
from 550 kc. to 30 mc., in four ranges.
The NC-81X is a special amateur model covering the following bands only: 1.7-2.0 mc., 3.5-4.0 mc., 7.0-7.3 mc., 14.0-14.4
mc. and 28-30 mc. The dial is calibrated in megacycles.
Posted January 10, 2014