Your RF Cafe
September 1937 QST
|Table of Contents|
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.
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.
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