Just wanted to report on my cheap and dirty 75A-4 AM filter. I am not the originator of this idea as I've seen past articles about it and I'm sure many of you have already done it. I bought an R-390A 16 KHz mechanical filter (F455N-160) at that auction place for about $30 and mated it using standoffs to a 9-pin plug that I bought here on the Reflector a few years ago (actually 10 of them) for about a buck or two apiece. It could not be simpler as projects go and it seems to work very nicely.
I see an R390A 20KHz filter just went for about the same price this week. I know a lot of hams use 75A-4 receivers on AM even though they were really designed for SSB. The R390A filters seem plentiful so if you have one lying around you can throw it in your A-4 pretty painlessly. With no filter it is a "dead" switch position so this way you can put it to use. I tried to find the 'net article I had read on this but couldn't seem to locate it so went from memory using two thin shielded wires to run to the top of the filter body. On the plug, pins 1 and 2 go to one side and 6 and 7 go to the other side of the filter.
73, Russ WQ3X
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