This was the last in the SW-3 line. I have a previous model
There were several versions of the National SW-3, and they have different power supply and coil (transformer) requirements. At first its a pretty daunting set of configurations to figure out, but luckily, using Google – you can find quite a bunch of great sites. This is one of my favorites:
I also have received the 1931 bound version of QST:
and it has several articles on receiver design in the 1930’s. Between new interesting tubes and just the design approach employed, it makes the 30’s one of the more interesting decades as far as technology is concerned. I think I’m mostly attracted to it because designers wanted to keep designs simple and with as few parts as possible – no doubt because we were coming off of a terrible recession. These receivers cost $20 – so you can see how much that amount of money could buy. What is astounding is the number of positive comments online regarding this SW-3 line of receivers. They are actually “beloved”.
One of the trickiest bits regarding these receivers is trying to find the coils. They command a pretty penny, so finding one set that has the top end of the broadcast band plus another that has 40 and 20 meters is a real find. I’d like to get the rest of the broadcast band, but the “orange” coils are hard to find.
Besides the wonderful and educational article on the SW-3 in the September 1931 issue of QST by James Millen, there is another in January 1931 by Robert Kruse – who covers what were the best design principles regarding receivers at that time. He covers the SW-5, which as the forerunner to the SW-3, and apparently, the SW-5 coils are interchangeable with the SW-3.
There are several coils that I wouldn’t be interested in, in fact – the orange pair is the only one I’d like – the rest are in band segments that no longer have any activity of any real note.