UBM Tech
UBM Tech

The R175A

-November 30, 2013

I think the most impressive RF choke I've ever seen was one that was made by the now defunct National Company, Inc. The part number was R175A. Just look at this picture of an R175A in service in a high power RF amplifier described by The American Radio Relay League.



The product line of that company can still be seen on line in their 1947 catalog. There is a photograph in there of this part's predecessor, the R175 which didn't include the 15 meter band capability. It looks a lot like this one, just with a little bit different coil structure near the top, please see this link.

The sheer physical size of this thing was impressive. Then one day, back when I was active in ham radio, I got into a QSO (remember that term?) with this fellow who had a transceiver in which he claimed that the RF choke that was used for the final power output stage was an R175A that was mounted vertically in a case, the transceiver's cabinet, which was only six inches in height.


That I knew couldn't possibly be so, but he insisted that it was and since he was local, he offered that I could come over to see it. I took him up on that.


The choke that I saw in there was most definitely not an R175A. It looked more like maybe an R154 or similar part (see that 1947 catalog). It was very much smaller, especially in its vertically mounted height.


No! He absolutely insisted that it was as he originally told me it was and there it was for me to see. End of discussion!

As Will Rogers put it, "It isn't what we don't know that gives us trouble; it's what we know that ain't so."

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