Hope everyone had a great Thanksgiving!
Today was sort of a good news/bad news day. As I’ve mentioned in earlier posts, I’ve been in need of a couple EMI filters for my antique radios. I was going to just order some off of Amazon, but today I remembered how a friend of mine had talked about making one out of old PC power supplies.
I have a bunch of these in a cabinet in my garage because I used to build a lot of vintage PC’s. So I did a little research and found out that on most power supplies, the EMI circuit is all the components before the bridge rectifier (black box thing in 4th picture). So I found a power supply with the right circuit, unsoldered the rectifier and soldered in two wires which then get soldered to a plug socket. These wires are on the end of the EMI circuit, so they provide the filtered AC.
I clipped off all of the other wires and jumpered together the green ‘Power Supply On’ wire with a black ‘Common’ so that the supply is always on when you plug it in. I did this by soldering a wire between the two points on the circuit board (black wire in the 5th picture). I had to do this because as you probably know, power supplies are turned on by the power button on your PC which connects to your motherboard. Since I wasn’t installing this inside a PC, I needed to make sure that I didn’t need any button to turn it on.
When I got it all put together and working, I came inside to test it on my GE-H32 radio. Unfortunately, it did nothing to cure the 60hz hum I’m getting. This means that there’s another source of AC inside the radio that’s causing the issue. I’ll probably have to pull the tuning chassis or power supply chassis back out of the cabinet and troubleshoot the problem.
However, the filter made a big difference for my Atwater Kent model 46 which lives in my bedroom. That radio now sounds really good when I tune in my transmitter, so at least all of the work wasn’t wasted.
You can see the Atwater Kent 46 in the post below…