I`v had what is for Me a bit of a breakthrough with my super-het project, an experiment that I`d been putting off and worrying about it`s feasability for the last few days has finally paid off!
namely the Coils and tracking for the mixer.
despite trying (and failing) to get any 1/4 inch Dia formers for the coils, I discovered some Cans in half a TV board that I`v had doing nothing for over a decade and stripped them down.
I also redesigned the entire front end of a Murphy 198 that I had for spares, fixed up a few problems it had, and got it working as just MW with bare bones basic circuitry (so no wave changer etc...).
I got some Coil data thanks to Harry Lythall
and had a go at making my own LO and Tuning coils to replace the MW coils in the 198.
when I powered it up there was silence until I hooked up the antenna (the ferrite rod antenna was now redundant), and I was on SW!
oddly there was very little in the way of Tuning needed to get some stations and all this worry I had about half a turn the wrong way and it won`t work etc... was ill founded.
in fact I find it to be Very forgiving indeed, reinforced by the fact that after re-reading Mr Lythalls data, instead of 27 turns tapped at 4, I`d done 4 turns, tapped and then 27, making 31 turns total!
(yeah, so I hadn`t had my morning coffee yet when I wound them :P )
I`v put a couple of pictures of these coils and my new SW radio below, the 1`st one is the Tuning coil (white wire is the antenna), the second is the LO and the complete absense of all the LW/MW stuff.
I`ll have a hunt around in the morning to try and find some suitable board, and then start work with the ECH81 using these Tried and Tested homebrew coils to make my Mixer, and then ultimately marry that to the other half of the super-het.
for that few that Are following my progress, take heart as the end is now in Sight!
edited to add: the above winding data takes you to SW, and the top end is roughly 10 MHz as I was listening to Radio Japan today on 9.8MHz and still had some cap left, and should go down to 4MHz.