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Author Topic: Johnson 500 Mod Transformer Issue  (Read 4197 times)
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WV Hoopie
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« on: May 20, 2005, 03:18:19 AM »

This evening I finally moved the last piece of the station into the new shack, a 8 X 12 building in the back yard. After wiring everything together and firing up the Viking 500 into a dummy load, I can hear a problem on the horizon.

The modulation transformer, an old Peter Dahl unit, sounds like a small audio amp. Inside that little shack, feedback is going to be an issue. If I crank up the audio gain on the Viking, the squealing starts. Short of drilling a hole through the wall and moving the PS/Mod outside, does someone have a cure??

The Oregon rains are scheduled for a two day outage this Saturday and Sunday. Time to start hanging wire from the trees.

Tnx,
    wd8kdg
            Craig
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Bacon, WA3WDR
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« Reply #1 on: May 21, 2005, 12:16:27 AM »

Hi Craig... maybe tightening bolts and whatnot will help, if such are accessible.

I had noise coming from a modulation inductor.  I put the thing in a box and packed it with fiberglass.  It helped.
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Truth can be stranger than fiction.  But fiction can be pretty strange, too!
WV Hoopie
Guest
« Reply #2 on: May 21, 2005, 02:39:48 AM »

Hi Bacon,

Today I spent several hours playing radio. Put a piece of 1/4 inch felt pad under the mod tranny and that helped. PS/Modulator is on the floor and decided to built a wooden wall around it also. I'm now able to increase the audio gain and back away from the D104.

The HV transformer likes to growl a little when cold, seems to quiet down as things warm up. The top of the perforated PS cover vibrates with the HV transformer (more feedback). Glad there isn't any rotating parts in there. Looks like more time will be spent tighting things up. Pain in the back side, should be working on the antenna.

Tnx,
     wd8kdg
             Craig
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WV Hoopie
Guest
« Reply #3 on: May 21, 2005, 04:21:03 PM »

The Mod tranny in the PS/Mod is the larger of two sold by Peter Dahl, the 29 pounder. Previous ower(s), repair person(s) replaced the original, reasons unknown to me. Rule of thumb #1, always blame it on someone else.

Laminations of the Dahl core almost rest on the chassis and are very close to the top of the perforated cover. So putting a felt pad under the Modulation transformer and leaving the cover off is real quiet. Didn't like the idea of leaving the interlock and shorting switch defeated with HV lurking about. So.............

Felt pad under and on top of Mod tranny, cover installed with 2X4 applying pressure between countertop above and perforated PS/Mod cover, and all of the above behind an enclosure. If it wasn't for the rain in Oregon I'd drill a hole in the wall and stick it outside.

Craig,
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WA1HZK
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« Reply #4 on: May 24, 2005, 10:12:11 PM »

I had to put a stack of rubber mats under my power supply to quiet it down. I'm using Peter Dahl iron also. My rig is mounted in a console made of steel so I had to isolate it.
Keith
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