March 1939 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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National Company, an early manufacturer of electronics
components for radio products, ran a series of unique advertisements in the ARRL's
QST magazine. Rather than using
precious cash for directly promoting specific products or product lines, company president
John Millen occupied full pages with text explaining why it makes the things it does and how
they can be used to solve problems or enhance performance. This article/ad on TMS condensers
(aka variable capacitors) was number 61 in the series, which means if they printed one every
preceding month, the first would have appeared in the March 1934 issue of QST.
National Company Advertisement
(Number sixty-one of a series)
Whenever we learn of a way to improve one of our products,
we like to incorporate the change in production units as rapidly as possible. Frequently it
is not practical to change already released advertisements or printed catalogs so that they
do not in their description of the product, conflict with the item itself in its revised form
and thus cause a certain amount of confusion.
For instance, in our catalog this year we specified the type 80 rectifier tube in connection
with our new type CRR oscilloscope. When these oscilloscopes were put in production, we found
that it was more desirable to use the 6X5 rectifier, rather than the 80. Consequently we did
so. Still another instance is our TMS condenser - in the original advertisement and catalog
listing we showed the condenser as having a long threaded bushing as part of the front bearing
assembly. In making these condensers, however, someone showed us that they could be improved
by omitting this bushing. Consequently, we did so.
We have been taken to task by a few of our customers on the two above mentioned improvements
that we made in production. We mention this now with the hope of forestalling any misunderstanding
in connection with an improvement program that we at present have under way for all of our
transmitting condensers.
We are in the process of increasing, wherever desirable, the thickness of the plates. This
brings up several complications, as the air-gap has to be slightly decreased or else the overall
length of the condenser increased. In the case where the overall length is increased, the
picture is complicated for the person who has laid out a transmitter around previously published
specifications of overall length. On the other hand, a decrease in the air-gap in some models
means a slight decrease in breakdown voltage, and thus, too, a deviation from previously published
specifications. This latter condition, however, is not necessarily universally true. In many
of the condensers, increasing the plate thickness and decreasing the air-gap by a corresponding
amount actually raises the breakdown voltage. This, of course, takes place largely in the
models with the longer air-gaps.
Changing the air-gap also affects the total capacity and, again, changes the past published
specifications. This latter matter of total maximum capacity of condensers, both transmitting
and receiving; opens up still another problem. It has been customary to classify and list
condensers by maximum capacity in round numbers; thus we refer frequently to a condenser as
being "100 mmf.". Actually, such is seldom the case in practice. Using a round number of plates,
the capacity is more likely to be anything but 100 mmf. If, on the other hand, the plates
are originally designed to have such an area and the air-gap is so selected that the 100 mmf.
condenser actually has a total maximum capacity of 100 mmf., then think of what is likely
to happen with the 50 mmf., the 75 mmf. or the 150 mmf., or any of the other such values ...
All of which means that where possible we add an extra plate and run the capacity somewhat
over the rated value. There are times, however, when it is more practical, and we feel more
desirable from the users point of view, to fall just short of the rated capacity than to run
far too much over.
Posted January 12, 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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