April 1942 QST
Table
of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
QST, published December 1915 - present (visit ARRL
for info). All copyrights hereby acknowledged.
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The National Company of Cambridge, Massachusetts, was one of
the first large distributors of electronics components and appliances. It began life as the National
Toy Company. Under the leadership of Mr. James Millen, W1HRX, National quickly became a market leader in designing and
marketing high quality radio products for both amateur radio operators and casual listeners of shortwave
radios. National Company very often ran full-page advertisements in the American Radio Relay League's
QST magazine, that were more in the form of an infomercial than pure product promotion. This
one, number 98 in a very long-running series, extolls the virtues of their famous NSM Modulator. The
majority of these ads were written my Mr. Millen, but in this case it was done by Calvin Hadlock.
A bit of trivia: National Company was the first paid advertiser in The Radio Amateur's Handbook.
National Company Advertisement
(Number ninety-eight
of a series)
These days when all sorts of amateur gear are being adapted to serve new defense purposes; we wish
to point out that the NSM Modulator has great possibilities as a public address amplifier.
With a microphone and suitable speakers, it serves the same purposes as a megaphone for calling and
giving instructions though its range and clarity put it in a class by itself. Its capabilities begin
where the megaphone's end. The peculiar fitness of the NSM for this job lies in its automatic volume
compression circuit. This circuit was originally designed to permit high modulation levels without danger
of overmodulation. With minor changes this same circuit provides a high level signal for loud-speakers
without danger of blasting. In our experience, this is a big help. When a microphone is used by a group
of people with different speaking habits and with no previous microphone experience, some sort of monitoring
is essential. An automatic device will do this job better than a manually operated control because it
gives consistent results and is always on the job.
The other features of the NSM also fit the specifications for a good public address amplifier. It
has an undistorted output of 30 watts and is entirely self-contained. A four position tone control cuts
highs or lows, or both, or leaves intact the normal range of 50 to 10,000 cycles. There are two input
circuits, one of which provides ample gain for any of the commonly used microphones.
In adapting the NSM for use with loud-speakers, the principal change is in the volume compression
circuit. This circuit is, in effect, a delayed AVC. In a transmitter, the delay voltage is taken from
the Class C plate supply, so that any change in plate voltage will automatically cause a corresponding
adjustment in the modulation level. For use with speakers, where there is no Class C plate supply, the
delay voltage can be obtained from the regular plate supply of the NSM through a suitable resistance
network. The actual change is very simple, and we will send specific instructions on request.
It is, of course, also necessary to provide an impedance match. The NSM is designed for a load of
1500 Ohms. In many cases, a series parallel arrangement of the speakers can be used to obtain this value.
A matching transformer can also be used of course, but if the speakers are located some distance from
the transformer do not use too low an impedance (such as voice coils in parallel), for the high current
at low voltage will waste a lot of power because of the voltage drop in the leads.
Calvin Hadlock
Posted May 11, 2017
Here are all the National Company advertisements I have:
- National's Company:
Merry Christmas and Happy New Year, January 1941
- National Company:
Noise Limiters, September 1950
- National Company: Modulators, April
1942
- National Company: Switches,
May 1939
- National Company: TMS Condenser, March 1939
- National Company: TVI, October
1953
- National Company:
Amateur Radio Activity, December 1952
- National Company: HRO-50
Receiver, May 1951
- National Company:
Noise Limiters, September 1950
- National
Company: Modulation, October 1947
- National Company:
Merry Christmas and Happy New Year, January 1942
- National Company:
Merry Christmas and Happy New Year, January 1941
- National Company: Switches,
May 1939
- National Company: AC Power Strip,
April 1939
- National Company: TMS Condenser,
March 1939
- National Company Catalog: NC80X
/ NC81X Receiver Advertisement, September 1937
- National Company:
IF Circuits, September 1935
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