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National Company Advertisement: TMS Condenser
March 1939 QST

March 1939 QST

March 1939 QST Cover - RF CafeTable of Contents

These 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.

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)

National Company Ad: TMS Condensers - RF CafeWhenever 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.

Here are all the National Company advertisements I have:



Posted January 12, 2017

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