The AM Forum

Another KW Matchbox goes under the dull scalpel.

Rich

Gee, what was this guy thinking (or smoking)?

73,

Bruce

Ummm... very clever?

This tuner has had it's relay removed.  There is only a single tap on the primary of the air wound input transformer.  The manual shows  two taps, one for receive and one for transmit, controlled by a relay.  It looks like transmit is a single turn and receive is four.

Anyone have any idea where to put a single tap?  Is there a benefit/need to have different taps for transmit and receive?

I have remembered that I already posted pictures of this.  Opened it up as I am finally able to fix it up and it was like it was the first time. 

Getting old sucks.


Rich
 

Gee, I was wondering what I'd do with my Johnson LP filter...

 ::)

DAMN.  :o


We gonna have to start a KW Matchbox rescue like they do with dogs.

Rich,

the tap with teh mo turns is your 300 ohm tap for your reciever. The single turn tap is your 50Ω for your TX for a transceiver.

the 50 ohm tap is important. the 300 ohm, not so much. on m HB coil i actually have 1 1/2 turns. JS clip lead a tap onto the link coil and move it around a bit with the unit set up for coax output into your DL.  (you gotta ground the outpoot terminal on the back.)

fire up at much reduced pow-pow-power and tune he matchbox for as low a swr as you can get. if it wont go dea nutz flat, unkey and hange your JS clip lead tap position a bit. You'll hit a tap position where you cant see the meter move. Thats 50 Ω, holmes. Solder in a new tap using
some flat copper or silver STRAP.   8)

unhook the grounding strap on the back unless you plan to keep on using coax output.

Just a guess....  50 ohm RX, 600 (or so) ohm TX?  Might match up nicely to 800 ohms......


--Shane

(guess Derb beat me to the post.....  :) )

That sounds like a very good plan, thanks.

Rich

Oh man..    I hate to see things like this.

I have rescued two KWs.  Always open them up and inspect before using..  This last one I got had the relay bypassed by someone jamming electrical tape into the relay.. LOL

Clark

When I first saw the hacked Matchbox above I thought someone put the directional coupler for the swr meter inside and I wondered why?  Oh brother  :(

I have a KW box and have been meaning to look inside before I try using it.  Last night I looked at the cabinet trying to figure out the easy way to open it up.  What's the right way to get inside?  I don't want to remove all the knobs or a bunch of screws that it turns out, don't need to be removed.  Unfortunately, it doesn't look like there's an easy way, like a single panel top that can be unscrewed and lifted off.

Thanks

Rob K5UJ

Nope, only way is to remove the bazzilion screws holding the cabinet together.  As I recall you do have to remove the knobs.

When you've taken out the bazillion screws, make sure you make note of the position of the knobs, or  turn them all in the same direction, before removing them. Failure to do so will result in the caps being in an unknown position when you replace the knobs, and this will lead to tuning problems.

thanks you guys--mine is one of the ones with the f.p. SWR meter and knobs for that so I'll have to be careful separating the chassis and back from the top/front.   also tnx for the advice on the knobs.  Mine was owned by a smoker at one time (probably all vintage gear was, since 9 out of 10 hams smoked  50 years ago) and I wanted to look inside to see if it is grunged up.  I remember when I was first getting started, I'd go to indoor hamfests and there would be a blue cloud hanging in the air.  Just about every ham had some kind of tobacco burning, pipes, cigarettes, cigars....in a crowd you had to watch out or get burnt by accident.

73

Rob K5UJ

Speaking of the bazzilian screws, some of mine no longer grab the metal, is there any fix other than using a larger screw?

Rich

Washers on the back?? .... maybee with a combination of longer screws...

klc

They actually thread directly into the sheet metal.  I do remember an old trick where you take a flat punch and punch around the holes which squeezes them smaller a bit.

Rich

PEM nut.  At your larger (not necessarily home cheapo / slowes type stores) hardware stores.  AND, they also sell a good assortment at the skate board shops, if you have any around....  The skateboard guys use them.

These are the same nuts that hold a lot of our gear together, that press into the chassis on the inside.

--Shane

How do you insert a PEM nut?

They are what's referred to as an "interference fit".

Slightly (and I mean SLIGHTLY) smaller diameter hole than the nut occupies, and the torque of the screw pulling it in seats it initially.

--Shane

Noooo... most press fit nuts, the brand name of the company that started the deal is PEM, also known as "clinch nuts" are not able to be seated by the screw at all.

The best way to do it is actually on a hydraulic press.
Lacking that, a good vise is second best.
Third best, and suitable for only some jobs is the visegrip pliers set on REALLY tight when you squeeze.

There are different depth clinch nuts, intended for different thickness metals. You definitely want one that is properly sized (shorter, not taller) for the thickness of your metal.

The hole you use is critical- the things work by displacing metal into a circumferential ring around the outside of the insert, when it is pressed. You want the nose of the insert nut to just fit into the hole - the knurled portion that does the metal displacement is wider.

Test on scrap of the same metal and thickness first, for best results.

There are some fasteners that pull when you insert, like pop-rivets. That's a different beast, and they may be fine for this, depending on the depth behind the schassis surface and the degree of flatness required above...

Check the web and PEM's site for more information and how to size and insert.

oh, they make 'em in stainless and aluminum, and regular steel too... I usually use the stainless, although the aluminium is ok fine in aluminum...

On occasion they just don't work right... be forewarned.

My old trick to fix that problem is a small flat piece with a clinch nut inserted, two 4-40 flat head screws with counter sunk holes to hold the piece in place behind the hole...

(easy to say, a fair amount of work to do when you get it done cleanly)


                  _-_-bear

PEM also makes a version with a floating nut that moves around in the housing to help with misalignment.

Use a sturdy C-clamp (like a 5" one) to set them and your good to go. There used to be a guy on ePay that sold them in 1000pc assortments for cheap. ($20ish) I'm not sure if he's still around, but that's where I picked mine up. 

I've got to find myself some of those!  Sounds like the ticket.....  I have a few chassis here that have flexed a bit over the years, and the threading of the screws has become "interference fit".

They don't sell them at the local skateboard shop, guess I'ma have to start looking around :)

I originally heard about them mounting the trucks to my skateboards in high school (grew up in / around Santa Cruz, Ca).....  Then, years later, I remembered them on my first big amplifier.

Ten more years later, I saw Rich Measures also advocated using them, with his Plywood Box amp.

--Shane


--Shane

[/quote]

PEM nut.  At your larger (not necessarily home cheapo / slowes type stores) hardware stores.  AND, they also sell a good assortment at the skate board shops, if you have any around....  The skateboard guys use them.

[/quote]

PEM nuts, a good idea.  I am not sure why I did not think of that, especially since I use them in my own products!  (www.fdatasystems.com)

Rich

Cuz j00 be habin a day like me!

--Shane