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Title: Johnson KW Matchbox Re-Build Post by: Steve W8TOW on March 12, 2013, 08:16:00 PM SO I've gotta tear apart my KW mbox to check for damage. A early
season lightning strike got my 600 ohm feeders & 1/2 of my dipole... The new 80m antenna is up, no rigs injured, but I better look inside the matchbox to be safe... One thing I've always wanted to do is "open-frame" the tried & true Johnson KW Matchbox.. I've gotta HB version hanging on the wall of the shack for my 160m antenna...no cover, just a couple of pretty caps & a BIG edge wound "L"... Anyone ever did this to the Johnson tuner? Mount it on a piece of aluminum sheet, and leave it unshielded? One note, with 600 ohm feeders, I've never had any RF back in the shack... My FS Meter sits pretty motionless, so the question is: "Is the shielding of the tuner really necessary???" 73 Steve "8TOW Title: Re: Johnson KW Matchbox Re-Build Post by: W2VW on March 12, 2013, 08:31:25 PM No cover necessary except to keep fingers away from high voltage.
Title: Re: Johnson KW Matchbox Re-Build Post by: Steve W8TOW on March 12, 2013, 08:47:59 PM Well, that was my opinion...I've monitored RF fields in the shack for 35 + years....
This is one of the cleanest installations I've ever been fortunate to have... SO...a pair of traditional "old buzzard" tuners on the wall is probably how I am gonna go! 73 Title: Re: Johnson KW Matchbox Re-Build Post by: K5UJ on March 12, 2013, 11:15:06 PM I always run mine with the cover off. I deliberately sought out one of the harder to find models (maybe earlier version?) that did not have the vswr meter in the can with the annoying cable tying the front panel to the chassis.
I prefer having it off so I can see the mesh on the caps which is easier for me to see instead of looking at the knobs. Also if a knob slips it's not a big deal. But the best advantage is clipping on additional capacitance (I need an extra 50 pF in series C on the lower half of 80 m.) is a breeze. In fact I operate my unbalanced L network tuner with the cover off for the same reason. Matching networks should be open in order to see what's going on inside. see photo Title: Re: Johnson KW Matchbox Re-Build Post by: Jeff W9GY on March 13, 2013, 07:49:27 AM Steve, I have a Johnson KW matchbox mounted on an aluminum chassis used at my Calumet QTH. (matchbox guts came from a hamfest missing the box) Nothing shielded and only a few feet from all the sensitive audio and RF gear. Never had a problem (80 - 15 M) 73 Jeff
Title: Re: Johnson KW Matchbox Re-Build Post by: Steve W8TOW on March 18, 2013, 04:24:54 PM BACK ON THE AIR!
Opened up the KW Mbox after an arc of RF shot up through it Saturday... (350 watts from the BC-610 will do that) ANYWAY, the problem found: The lead in from one of the antenna terminals on the back of the Mbox goes to the rotor of a cap. Well, it used to...It was no longer connected to the cap but a pool of solder was in the bottom of the cabinet. Lightning had come in , a small corona was cleaned from the cap, and the lead re-soldered! There WERE some hints this was the problem. I had attempted to use my 160m 1/2 wave dipole as a 1/2 wave end fed on 75m...it would resonate when connected to one of the ant terminals, but not the other...since it was not connected to anything! ALL IS WELL, no cover, and soon to just be mounted on the wall. Anyone want a KW Matchbox cabinet? I'll bring it to Dayton :) 73 Steve 8tow Title: Re: Johnson KW Matchbox Re-Build Post by: N0WEK on March 18, 2013, 06:17:45 PM Might be good to keep the cabinet, it'd be a shame to orphan the thing without the cabinet. You or someone may want to restore it to original someday.
Title: Re: Johnson KW Matchbox Re-Build Post by: W2JBL on March 18, 2013, 07:46:11 PM having it open like that you could cook hot dogs by putting them inside the coil while you cotton' pick'n AM'ers make your 45 minute long transmissions...
Title: Re: Johnson KW Matchbox Re-Build Post by: Steve W8TOW on March 18, 2013, 08:48:36 PM Good point...I can just add the cabinet to the "pile".. :) AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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