The Johnson 275W Matchbox Antenna Tuner

I had purchased a Johnson Matchbox from an estate a while back & decided that while I was home with the flu I would open it up and check on its condition.

The Johnson Matchbox is found most commonly in two versions, the smaller “275W” unit and the larger Kilowatt Matchbox. Why did I use quotation marks around 275W? Well, these units were manufactured back in the good old days when men were men and transmitting voice meant using AM, not single side band. The conservative rating of 275W of AM translates into roughly 800W of peak SSB  (Not really but close enough so you get the idea)

Unlike many who own a Matchbox I was hoping to keep it 100% original and that it would contain all its original components, including the antenna change-over relay and wiring for the high-impedance receiver antenna connections. I plan to use this Johnson Matchbox with a Heathkit AT-1 transmitter and Hallicrafters SX-25 receiver so the inclusion of an antenna change over relay and 300 Ohm receiver connections will make life MUCH easier. Something I didn’t realize until I had the unit apart (There are a LOT of screws holding this thing together) is that there is also a receiver control contact on the relay to break HT and mute the receiver during transmit which will work with my SX-25.

An initial inspection showed that the only modification was a small piece of plastic wedged into the relay contacts that held the relay in the transmit position. It was easily removed and the relay coil and contacts tested for continuity. The contacts seem a bit dirty which, from the little I have read online, seems to be a common problem.

Once the relay contacts and band-switch are cleaned I will button the unit back up and connect it to the loop antenna I have recently run around the eaves of the house. The loop has been a huge improvement to the long-wire and magnetic antennas I have run in the past, at least as far as reception goes … but that is a topic for another post.

Owen Morgan, KF5CZO, is a regular contributor to AmateurRadio.com and writes from Texas, USA. Contact him at [email protected].

Leave a Comment

Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter
News, Opinion, Giveaways & More!

E-mail 
Join over 7,000 subscribers!
We never share your e-mail address.



Also available via RSS feed, Twitter, and Facebook.


Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter

 
We never share your e-mail address.

Please support our generous sponsors who make AmateurRadio.com possible:

KB3IFH QSL Cards

Hip Ham Shirts

Georgia Copper

Ham-Cram
Expert Linears

morseDX

Ni4L Antennas

N3ZN Keys

West Mountain
R&L Electronics


Do you like to write?
Interesting project to share?
Helpful tips and ideas for other hams?

Submit an article and we will review it for publication on AmateurRadio.com!

Have a ham radio product or service?
Consider advertising on our site.

Are you a reporter covering ham radio?
Find ham radio experts for your story.

How to Set Up a Ham Radio Blog
Get started in less than 15 minutes!


  • Matt W1MST, Managing Editor




Sign up for our free
Amateur Radio Newsletter

Enter your e-mail address: