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Author Topic: Reviving and old Johnson Matchbox  (Read 642 times)
AC0DV
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« on: February 22, 2006, 03:55:16 PM »

Just picked this nice old tuner up. (Actually it's the Nye-Viking version. "LITE")

I'm using it on a 80m full wave horizontal loop fed with 450 ohm ladder line.

It looks fairly clean... it tuned up on a few bands and then it started humming... the SWR would move down a little while tuning... then it started "humming" and the SWR would go WAY down... then go back up after a few seconds to where it was before the humming started.

(I'm using 10 watts AM output during tuning.)

Is this what is known as "arc-ing"? (Even with low power?)

Anyway... when I went back to the other bands it sometimes worked... sometimes had the "humming/SWR" effect all over again... intermittent.

I suspect it needs some serious cleaning. I'll take it apart and use a fine brush around the tuning caps and something non-abrasive on the coil... see if that helps out.

Any other advice on reviving this old but very worthy piece of hardware?

When it did tune okay... it "felt" better than my MFJ-929E tuner. (Plus I'm looking forward to getting rid of the balun I use with the MFJ.) I had 1 QSO on 20... and it was working well... then after a few minutes... at a "good" SWR... it started up the humming/SWR bit again... doesn't look that dusty inside... but looks can be deceiving.

Since there's not a lot of parts in this type of tuner... I suspect (hope) it's only old dust etc... and that I can make it happy by giving a major cleaning.

Thanks,
Keith -- AC0DV
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KA5N
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« Reply #1 on: February 22, 2006, 04:27:33 PM »

The first thing I would do is take the cabinet top off and inspect.  There may be signs of coil overheating, the plastic parts of the coils may have melted and sagged.  A soft paint brush is enough to clean out dust.  I wouldn't use a wire brush.  I am not sure about the NYE version but the Johnson matchboxes had a changeover relay.  This is not needed with a transceiver and the contacts should be wired around or the relay jammed in the closed position.  There could be a bad contact in some of the coax connectors or interconnecting cables.  Other than the relay there shouldn't be anything that hums.
Allen
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AC0DV
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« Reply #2 on: February 22, 2006, 04:52:40 PM »

Actually the "hum" is from my computer speaker RFI... very frightening sounding. Sounds like a Van-De-Graaf generator. BUT If I turn them off... there is no audible "hum"...

BUT I still get the weird SWR swing to LOW... then back up to normal. (It's weird... it either "happens" or it doesn't. If it starts... you have to back of the setting until it stops.. then slowly move forward again... I think it's doing some kind of oscillating... and my brain thinks of little dust particles causing gew-gaws to motivate in the thingamajob.)

NOTE: I'm a physicist. Can you tell?

The Nye-Viding doesn't have the relay... about the time they took over from Johnson... most people were using transceivers so they made the relay an "add-on".

So the only parts in this puppy are the caps and the coil. (And a few minor parts for the SWR meter. But even an external meter has this reaction.)

I'll clean it and post my results. (After I've rested... I've been working on this for 7 hours.

Well not JUST this... I had to prune 9' off of my horizontal loop... to see what that would do since it was 290' long... I had to measure up my feedline and make sure it's a good length...  (43 feet) and had to add a pulley to one of the corners of my loop so that I can add a counterweight to allow for tree swinging.

All after tinkering with the Matchbox for awhile after it came fedex this morning.

Phew. Now I'm tired. Think I'll take a break.

Thanks,
Keith -- AC0DV
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AC0DV
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« Reply #3 on: February 22, 2006, 04:55:50 PM »

OH.. and BTW... I did a quick visual inspection of the insides. Very clean other than some light dust. (And perhaps the silver on the coil is tarnished?)

No obviously melted doo-hickies or whiz-gongs.

tx -- K
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AC0DV
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« Reply #4 on: February 22, 2006, 10:12:03 PM »

AH HA! EUREKA. And other such exclamations. FOUND IT!!!

There was a "modification" to the box.

This box was designed to allow balanced line OR unbalanced line. To hook up the balanced line... you hook up to the two terminal posts. (As is obvious.)

To hook up coax... you hook up the center conductor to 1 post... and the coax to the ground... and you ground the other post.

Someone had installed a coax connector onto the chasis... and grounded 1 of the balanced line terminals. (Effectively making it an un-balanced ONLY Matchbox.)

SO... there I was hooking up balanced line.. by grounding 1 side to the chasis.. and the other to a live post. RFI CITY!!! Worse than anything I've ever heard. (Enough to actually make me nervous. Okay.. scared... you should have HEARD the RFI/HUM/NOISE. It deactivated my USB computer keyboard.)

Anyway... I removed post to ground... and deactivated the coax connector.

Hooked up... it tunes 80,40,30,20,17,15,12, and 10.

Unfortunately... it tunes 80 up to about 3.885 with an SWR < 1.5..... up to 4.0 MHz with a SWR of 1.6 to 1.

(Dang it... so my solid state rig goes to half power if the SWR is above 1.5.)

But... I'm still working on it....

--Keith -- AC0DV
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AC0DV
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« Reply #5 on: February 27, 2006, 03:06:08 PM »

Grabbed 2x 680 pF (6 KV) caps from a local electronics supply. and stuck them across the output variable cap....

(It was $3.00 for 680pf... 6kV... $20.00 for 500pF 15kV...)

The 680pF caps works just fine... gets the SWR down to 1.1:1 on the top of the 80/75M band. (ANd 160M... but the antenna won't do topband well.... so who cares.)

Good deal!!! So I can use this tuner for 1.1:1 SWR across the entire band.

I feed MUCH better using this venerable tuner over an MFJ high loss T-Circuit with a balun.

Now I need to find a relay... so I can have a quick switch for this band.

Happy Happy... Joy... Joy.

-- Keith -- AC0DV
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