The AM Forum

THE AM BULLETIN BOARD => Technical Forum => Topic started by: W3SLK on May 02, 2023, 11:01:39 AM

Title: HRO-50 D Coil Set
Post by: W3SLK on May 02, 2023, 11:01:39 AM
I have since retro-fitted a new audio transformer in my HRO-50 and it plays nice now. I have good results on 40M both in general coverage and band spread, (coil set C). When I use my coil set 'D', I am spot on in general coverage. But when I use it on 75M band spread, I get 4.0Mhz where it is supposed to be but regardless how hard I try, 3.5Mhz never seems to go below 3.7MHz. I thought I was hearing the signal when mixed with the HFO at 3.955Mhz. but I can never find the fundamental freq. at 3.5Mhz. I think the coil set was originally part of a R-460/UR receiver set that was made for the USCG. It has a tag "R-459/UR, Number Set: 61 with the 'D' stamped in the middle of the panel like the others. I was going to send an email off to KM1H but thought I would try here first. Any suggestions are greatly appreciated.

Title: Re: HRO-50 D Coil Set
Post by: W3SLK on May 04, 2023, 06:57:15 PM
Huzzah! Problem solved! I went back to square one and checked the tracking on the general coverage since that effects the band spread. All good, from 1.8Mhz to 4.0Mhz even at .15 uV! It tracked everything in between so I knew I was dealing with something specific in the band spread. Somehow I managed to get it so it would receive when the freq. gen was at 3.5Mhz it would hear it at 3.6Mhz. So I started incrementally shifting it downward. At one point I got to where I had more travel left on the trim capacitor, but the frequency started tracking upward again! So I pulled the coil set out of the radio and disassembled the coil set for the HF oscillator. I turned the trim pot and noticed that the end section rotor was not tracking properly and was shorting out with about 1/3 remaining of total rotation! So I break-out the dental tools and magnifiers and tweak that rotator plate back so it is on a true plane. Put everything back together and about 3 cycles back and forth of 3.5Mhz and 4.0Mhz and it came right in! Another weird one for the books. As my friend Sai would say, "When you think you have seen it all today, wait until tomorrow!"
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