Latest addition to my ‘Codar Project’ is to try to get hold of an old Codar PR30 preselector to use with the RAT5 receiver. These are not easy to find, so I put an appeal on the Facebook page to see if anyone had one lying about. A big thanks to Evan who responded, he had an old rusty one in the shed with a load of other junk and kindly sent it to me.
When it arrived I had a look inside, it was like new! The case was badly rusted, but that just needed cleaning up and a fresh coat of paint.
Originally, the PR30 used an EF183 valve, but of course, this means building a PSU to power it or somehow connecting it to the Codar AT5 PSU. Instead,I decided to change it by building the later PR40 circuit, which used a FET instead of the valve and runs on 12v. I built a printed circuit board for the first time in many years and mounted it using the same holes as the transformer would be. There were several versions of the PR30, some with PSU and some without, mine was originally powered by a Codar Valve Receiver.
I had to remove the anode choke and use it in the collector of the output circuit. The new circuit works fine! The front end stayed exactly the same and testing it through all the bands gave a very sharp peak in selectivity. The gain control gave ample (if not too much) gain throughout. I changed the old coax socket to a phono socket and replaced the screw on antenna terminals with another phono socket. These will work fine on Topband! I also replaced the switch on the rear panel, this originally shorted one of the aerial connections to earth so that you can use a dipole or wire aerial. Now it is used to switch through the aerial with or without the preselector, which is very useful.
To finish off,I added an LED indicator, new knobs, good clean and a coat of paint!
Now it matches perfectly with the AT5 and RAT5…