johnson matchbox-275watt version

[ve6pg]

..matchbox in the mail, on it's way....question is, i know it states it is the 275 watt version, but i'd like to know how much this thing can handle....275 AM carrier, plus peaks, or what?..
..tim..

..sk..

[K5UJ]

The way it is supposed to go is 275 w. input carrier, making it supposed to be ~ 180 or 190 w. and ~ 700 to 800 with modulation but of course YMMV with stuff like the feedline, Z at the back of the box, and all that.

rob

[K1DEU]

And due to a lack of C on 80. when using it on 80 you may have to derate it, if you hear it becoming a flash box on voice peaks.  Dr. John, K1DEU

[KA7WOC]

And everything being equal I can run just under 450 'Drake Watts' into mine before it flashes on 75 meters.  Ant is full wave loop fed with open wire.
 

[ve6pg]

..received the box..looks ok..different than the dwg though...input for coax antenna is a so239...relay inside has cardboard between the contacts...cant seem to tune the owl on 80...using a 160m loop, 600ohm feeders...i dont need the internal relay, as i use an outboard one fer the viker...did this thing ever come with 2 so239s?....bama dwg shows hooking up a coax antenna line to the long wire post...any ideas?..
..tim..

..sk..

[K5UJ]

At a minimum you should have the UHF jack connected to a couple turns on the link with the other end grounded.  Your "band switch" should switch the taps on the coil with each end of the coil going to a section of the first air variable (the one labeled "tuning" IIRC) then on to the four section air variable (matching) which feeds the lines going to the pair of feed through binding posts for the wires of your balanced feedline.   That's really all you need, assuming you got it to use with balanced feed. 

The relay was used for switching the link tap.   Originally there was a high Z link in addition to the one for transmitting, that the relay would switch to on receive, because in the 50s (as well as today if you are vintage enough), there were receivers with 300 ohm or higher balanced antenna terminals on the rear panels instead of coax jacks.   The rx link tap went to the relay and then to a terminal barrier strip on the rear panel.  Often you get matchboxes in which someone removed the relay.   On the KW version, the relay is actually a nice Johnson QRO tx relay, good for use in a separate project box. 

The second UHF jack was just jumpered over to one of the balanced feedline binding posts, or the single wire post, can't remember which.  You also should have a ground lug on the back panel.  That's about it.   Not sure why it won't tune ur 160 m. loop on 80; maybe your feedline is some weird length.   The KW version has more Z range.  Be sure to ground the matchbox using the rear panel lug.

Rob