Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
KW Matchbox




 
The AM Forum
September 20, 2018, 03:14:29 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: KW Matchbox  (Read 1540 times)
0 Members and 1 Guest are viewing this topic.
K9ACT
Member

Offline Offline

Posts: 12


WWW
« on: April 16, 2018, 10:03:55 PM »

Two questions on KW Match Box just donated to my shack rebuild.

After removing a zillion screws, I still can not figure out how to open it up to answer the next question.

Connecting antenna analyzer to RF input and ladder line to output, it seems to work just fine.

However, looking at schematic, it seems like with no power to the relay, there should be no connection at all.

Is it not safe to assume that the relay is normally open with no power, i.e. faults to receive mode?

Thanks,

Jack
Logged

Astronomy, Beer, Cheese, Fiber, Gems,
Nature, Radio, Sheep, Sausage, Silver
         http://schmidling.com
KA2DZT
Member

Offline Offline

Posts: 2132


« Reply #1 on: April 16, 2018, 10:13:04 PM »

Just worked on one, the smaller 275 watt model.  You have to remove the knobs to open the unit.  The one I have, the relay terminals were soldered together by someone.  Probably something similar with your tuner.  So the relay doesn't work.

Fred
Logged
N1BCG
Member

Offline Offline

Posts: 592


« Reply #2 on: April 16, 2018, 11:02:41 PM »

Both the kw and 275 Watt versions of the Matchbox were designed in the days before transceivers, so it was typical to have a separate receiver. Also during that period, receivers commonly had screw terminals for antenna and muting connections. The matchboxes provided muting contacts as well as a switched antenna connection.

This was all very handy, but the additional functions became obsolete if the tuners were used with transceivers, this the common practice of bypassing the relays.
Logged
K9ACT
Member

Offline Offline

Posts: 12


WWW
« Reply #3 on: April 16, 2018, 11:33:59 PM »

Just worked on one, the smaller 275 watt model.  You have to remove the knobs to open the unit.

By that I assume you mean also the nut that secures the shaft to the panel?


js
Logged

Astronomy, Beer, Cheese, Fiber, Gems,
Nature, Radio, Sheep, Sausage, Silver
         http://schmidling.com
KA2DZT
Member

Offline Offline

Posts: 2132


« Reply #4 on: April 16, 2018, 11:44:36 PM »

No, that is a bushing that remains on the panel.  The shaft slides through the bushing.
Logged
K9ACT
Member

Offline Offline

Posts: 12


WWW
« Reply #5 on: April 16, 2018, 11:46:35 PM »


This was all very handy, but the additional functions became obsolete if the tuners were used with transceivers, this the common practice of bypassing the relays.

I won't be using a transceiver so I am hoping to use it more or less as intended and it seems like I should be able to use the relay for antenna switching without having to use and addition Dow type.

However, as the receiver input is not 300 ohms, it's not obvious how to connect it without getting into the box.  It probably has been bypassed as has been suggested.

Right now, the only receiver I have is an RTL Dongal which I will probably replace with a SoftRock.

As a point of interest, we had a disastrous just before Christmas which leveled my workshop/lab/garage/ham shack and barn.  60 years of treasures up in flames and I am starting from scratch.  Reminds me of my novice days in high school.

Jack
Logged

Astronomy, Beer, Cheese, Fiber, Gems,
Nature, Radio, Sheep, Sausage, Silver
         http://schmidling.com
KA2DZT
Member

Offline Offline

Posts: 2132


« Reply #6 on: April 17, 2018, 12:20:43 AM »

Wow, sorry to hear of your loss.  Hopefully you can get a station back up and running.  You'll never replace everything that was lost.  You can only pick up the pieces and try to move forward.

Hope no one was hurt in the fire.

The receiver terminal is connected to a tap on the coil.  You can move the tap to lower the receiver impedance.  Although it probably is not that critical.

You're right about the Dowkey relays,  They are expensive nowadays.  I'm still using my Dowkey from my novice days.  That was 57 years ago.

Fred
Logged
K9ACT
Member

Offline Offline

Posts: 12


WWW
« Reply #7 on: April 17, 2018, 01:03:51 AM »

No, that is a bushing that remains on the panel.  The shaft slides through the bushing.

Had me fooled.  Got it apart in about 5 mins.  I had only put back about 10% of the screws so it went pretty quickly.  Never saw so many useless screws.  Guess they were really paranoid about TVI back then.

The relay has been disabled so I will have to study it carefully to get it back to the original arrangement.

Thanks for the help.

Here is a link to some of my stuff pre-fire...

  http://schmidling.com/radio.htm

js
Logged

Astronomy, Beer, Cheese, Fiber, Gems,
Nature, Radio, Sheep, Sausage, Silver
         http://schmidling.com
K9ACT
Member

Offline Offline

Posts: 12


WWW
« Reply #8 on: May 02, 2018, 01:14:54 AM »

The schematic for the KW Matchbox shows a resistor and capacitor in series with the 115V AC to the antenna relay and a 16 mfd cap across the relay.

The series resistor is labeled SR and the parts list calls this a selenium rectifier.  I presume this means that the relay is DC but what's with the cap in series?  Why would the relay stay closed?

js

Logged

Astronomy, Beer, Cheese, Fiber, Gems,
Nature, Radio, Sheep, Sausage, Silver
         http://schmidling.com
W3RSW
Contributing
Member
*
Offline Offline

Posts: 3238


Rick & "Roosevelt"


« Reply #9 on: May 02, 2018, 03:47:18 PM »

In the smaller version matchbox I picked up in Baltimore some years ago I found that the DPDT relay had one half inch lengths of clear tubing placed over the receive only (upper) contacts. Neat way to keep it on one setting even though not energized. Since thick tubing was just the right size, it Forced the armature to be closed on other side too yet did not overly stress the armatur blade tensions.

Tubing looks to be gas line grade and thickness or possibly heart bypass, real surgical tubing.  ..a decent analogy there somewhere.  Grin

Obviously a method for getting proper relay deactivation without wires or soldering. Instant demodification by simply removing tubing. There has been constant tension on the return spring all these years, though probably not enough to hurt the spring with such small travel compared to its initial length.

Iíll get a pic of it.
Oh I see mm gradations on tubing. Mystery solved.



* D840595E-E668-468B-9B1A-D910CB0556A2.jpeg (2213.23 KB, 4032x3024 - viewed 120 times.)
Logged

RICK  *W3RSW*
W4EWH
Member

Offline Offline

Posts: 764



« Reply #10 on: May 04, 2018, 12:29:18 PM »

I owned a KW Matchbox years ago, and always admired the beefy construction. I now use a Heathkit SA-2060A, and aside from taking forever to get from one end of the rolling inductor to the other, it performs well.

I wonder, now, with compact capacitors, modern insulation, and so forth, if the KW Matchbox is still worth the prices sellers ask.

W4EWH
Logged

Life has a curious way of evening out
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1868


Making AM GREAT Again!


« Reply #11 on: May 04, 2018, 08:56:05 PM »

I paid a hundred bucks for my kw matchbox and the matchbox 275 was given to me.

I'm happy with the price!

--Shane
KD6VXI
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.052 seconds with 19 queries.