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THE AM BULLETIN BOARD => Technical Forum => Topic started by: flintstone mop on March 29, 2022, 11:12:20 AM

Title: EF Johnson KW BOX
Post by: flintstone mop on March 29, 2022, 11:12:20 AM
I have a EF Johnson KW matchbox.
I modified it for use on 160M from ER142. 4 ea 50pf doorknobs @ 15kv across the main coil and there I am on 160M.
Lately the old girl has gotten shakey putting allowed AM carrier to the box. Tuning, with the probably destroyed (made in Ukraine) Rig Expert antenna analyzer ZOOM.........shows me an excellent match. Tuner working fine all winter. Many QSO's. Now SWR suddenly jumps up. Put that system back on the analyzer and a little working of the tuning knobs and I can get to a perfect match again.
Sprayed DeOxit on the slider contacts on the (stator??) the sliding GROUND and a little TLC on those contacts helped somewhat, but no guarantee if it will hold the adjustment and decide to drift off-resonance.
Nothing is loose or flakey. Capacitors are bread slicers that are probably almost as old as I am(????) Nothing arced out or arcing when the tuner decides to work. Can't depend on her no more.
My HB tuner from K1JJ fame is still working and solid. So, it's not my antenna system crappin on me. It just seems that the EF Johnson gets a little more juice to the ether than Tom's design.
"Seems" like better signal reports since using the Johnson.
Any ideas?
Fred........................I might decide to build this monster tuner down the road and have a tuner shootout using a field strength meter and the camera on my cell to see any increase / decrease

Title: Re: EF Johnson KW BOX
Post by: Detroit47 on March 29, 2022, 11:38:20 AM
What monster tuner are you thinking about building?

Johnathan N8QPC

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on March 29, 2022, 05:27:23 PM
the one in the pictures in my post.......
A Richard Measures creation


Title: Re: EF Johnson KW BOX
Post by: W3SLK on March 30, 2022, 06:24:44 AM
Fred, first off it is good to learn you are vertically polarized and not horizontal. I prayed for you and your family every day and will continue to do so!
I am going to build a similar tuner but use roller inductors. I have a set-up for Arduino so I will use that to measure, control, and hopefully remember settings. KA4CID has an excellent website where the concept of a 'true balanced line tuner' was conceived by E.F. Bigbie, W4MMQ(SK),
I would also read up on the notes by L.B. Cebik. W4RNL(SK). I hope to hear you on the air again!

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on March 30, 2022, 11:38:49 AM
Thank you Mike for your prayers. It was a wrinkle in life. Missed out on almost 3 mos couldn't work. But back as new. I'll look over the  links for the tuner. I'm sorta situated now to be ALMOST mid-west. I can communicate  with 1885 ops but that causes grief when the mid-west guys are on 1880 and vice versa. I'll always be trying to make something happen on 160.....75 gets a little competitive.


Title: Re: EF Johnson KW BOX
Post by: Opcom on March 31, 2022, 12:11:52 AM
The only experience I have with a tuner changing tune or messing up is when a large mismatch is being corrected and there is a core-type balun on the antenna side. The ferrite gets hot and it flakes out. Mine recovered but do they always recover when cooled down? The other time was mica transmitting caps with too much current or in a frequency range they didn't like.

Your 'monster' looks to have the balun on the 50 ohm side, so when the VSWR is good  then it won't get hot.

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on March 31, 2022, 10:51:14 AM
Thanks Patrick,
The monster tuner pictured is in a future building stage.
The tuner I'm dealing with that has become intermittent is the venerable EF Johnson KW Matchbox. I explained how I got it to 160M, from an ER mag idea. After many months of succesful 160M QSO's and 250W carrier it now has gotten intermittent tuning.
I built the original K1JJ tuner and it's steady as a rock. So it proves out that my ladder line fed VEE is good.
I'm thinking there is something wrong with the sliding contacts for the ground side of the bread slicers and how to refurbish them.


Title: Re: EF Johnson KW BOX
Post by: Opcom on March 31, 2022, 10:17:18 PM
There's this article. i misspoke on what it exactly sais before so judge for yourself.. No idea if this makes sense or is a good idea.

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on April 01, 2022, 10:38:20 AM
VERY interesting............this is the answer to flakey connection. Thank you
I'll print the attachment out and give it a shot


Title: Re: EF Johnson KW BOX
Post by: Opcom on April 05, 2022, 02:51:02 AM
I hope it might help with the idea, tho' the KW size cap current might prefer something more skin effect friendly like copper braid or solderwick than the article's #27 vfo wire  :-) Good luck!

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on April 06, 2022, 10:13:56 AM
Thanks Patrick
I finally had my private matchbox shoot-out between the EF Johnson and the old standby from K1JJ and his tuner. The K1JJ had that little bit extra, a little over a needle width. in signal strength over the EF Johnson Matchbox.
It was not a scientific approach using a calibrated FIM. Very simple basic MFJ style field strength meter. I might do it again using an SDR and a different receive antenna and look at the signal on a spectrum analyzer type of display, that SDR's give.
Kind of makes beating on the EF Johnson a waste of time; as the tuning range within some HF bands is limited, by not having a tuned input. Anneck (?) German made Antenna Koppler was sort of a copy of the EF Johnson pick-up coil over the final larger coil and that strange capacitor on the output and includes input tuning enabling the Antenna Koppler match all 8 HF bands.


Title: Re: EF Johnson KW BOX
Post by: W2JBL on April 14, 2022, 08:43:00 PM
  I have used a KW Matchbox for a good 50 years and only had one failure, which might be your problem. The unbalanced coax output has an SO-239 with a bakelite center insulator. Mine became conductive unbeknown to me until one day in the 90's when it exlpoded in  flames under 500 watts AM. Maybe yours is leaking (carbon tracks formed inside the insulation) causing trouble. I replaced it with an SO-239 with teflon insulation. Today that same tuner handles the full output of my Johson Kilowatt, and 4-1000A linear at full strap with 5.2KV on the plate.

Title: Re: EF Johnson KW BOX
Post by: flintstone mop on April 15, 2022, 04:57:04 PM
I'll check that out Thanks for a reply.
My problem seems to be the TRANSMITTER variable cap. The sliding contact for the ground contact seems to be intermittent. After working the capacitor a few times it works and I'll have the 1:1 match. Put some power to the tuner and works perfectly. Let it sit a few days and the same problem comes back.

Title: Re: EF Johnson KW BOX
Post by: N7ZDR on June 05, 2022, 07:03:15 PM
In the drawing above I appears that if we rotate the knob it will wind the wire up! I guess if I had stops on each side it would work great. No stops on anything I have so I see a broken wire in a couple weeks time for me.
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