Even though we had to endure a 40C plus heat wave over the last few weeks I got into the shed early and drilled some PCB including the one above before it got too hot. I spent all of Saturday assembling and testing and it works quite well with about 20db of conversion gain. I had to make some modifications on the fly during testing and debugging but no major changes. As expected, and due to the extra filtering, the unwanted signals at the 28MHz I.F. output are less than they are with the simple SA-612 converter described further up this page.
I built this receiving converter in December of 2018. I found the circuit by doing a Google search which led me to the ON6MU web site. Actually I found many circuits but for some reason this one appealed to me. Again I made a PCB using Express PCB and the iron-on method. The 50MHz RF & mixer stage is an SA612 integrated circuit followed by a 2N3904 post mixer amplifier at 28 MHz. It's debatable as to whether the 2N3904 stage is required in my case but may be helpful if the receiver being used as the tunable I.F. does not have an R.F. amplifier at 28MHz.
I have not enclosed my converter in a case as yet but I have tested it by listening to the local six metre beacon some 30 kilometres away. I can hear the beacon without an antenna!
To suit my needs I did change some component values such as the output coupling capacitor. It is 10pF in my version whereas it was 270pF in the original. I found the lower value reduced the no signal noise floor in my receiver but did not reduce a signal's strength when one was present.