[Boatanchors] National SW-3 adventures

[Bill Cromwell]

Hi Everybody,

I have a National SW-3 that was kindly loaned to me with some sample
plug-in coils. The idea is that I am going to use this radio to make
new coil forms as per sample and test them. The first step was
assembling a power supply which is not all that difficult. The second
step is getting the radio to receive with the pair of coils that were
supplied. Friday night I finally completed step two! Over the years
there have been numerous repairs and possibly modifications as
evidenced by the many solder tracks and tacked together parts.I found
the one healthy looking cold solder joint that was depriving the
detector of plate voltage and then we had signals coming in. The radio
may have been "inoperable" for a while or the solder joint may have
opened during shipping to my house.

The SW-3 is a 1930s receiver - a three tube regen that would be 1-V-1.
I had nothing to do with the design or construction of this radio but
the rush of getting that signal into the phones and all of the
controls doing more or less what they should was about the same as my
homebrew projects. I already have the first, hand made coil forms
under construction and it will be great to get on with this project.
The idea is to make new, plug-in coils and new, plug-in coil forms
available. National used a non-standard six pin arrangement and those
will be first but there is no reason other pinouts cannot be produced.
People with fabricating skills can obviously make their own. I plan to
make details available so that anybody who wants to can roll their
own. The same approach will work for the standard four, five, six, and
octal pinouts for homebrewers.

270 degree slf air variable caps anybody? That's what the SW-3 has and
270 degree rotation tends to spread the tuning range out over and
above reduction drives. The straight line frequency label might be
more aptly named straightER line frequency. The tendency to bunch up
the stations at one end of the dial is greatly diminished. In 1933
that probably was as "staright line" as it gets. "SLF" depends on too
many other things to be an absolute expectation. I'm thinking through
the process to make some of these at least for my own use. The ones in
the SW-3 are *nice*.

Radio operators accustomed to digital readouts and shaft encoders who
have never used gear like this may be in for some surprises...
hopefully all enjoyable ones. Radios like this have to be *operated*
with both hands and your head - I've said that before. No computer is
going to operate any part of it for you (even though some hams have
used regens on PSK, etc). But those signals are there loud and clear.

73,

Bill  KU8H