Wednesday, 8 June 2016


This blog is about how I refurbished the points and adjusted the spring tension on my Chrome Covered NATO morse key.

This key, based on the swedish design key, ( Lennart Petersson )  ( also known as "the swedish pump key")  uses a spring plate for the support and spring tension on the main rocker/sending arm. There is a spring tension adjuster, using a spanner and an allen key, that can only be accessed by removing the cover.  

. The switch on the front of the key, is for switching the key "out of circuit" of any transmitter, thus giving the operator control, and can prevent accidental keying by knocking the key.

The key was made by  Marconi S & R systems Ltd, from the late 60`s onwards, and also by Pryce Edwards Ltd. The key is a heavy one !... it weighs in at about 3.5lbs ( or 1.6 kg ).so it "sits" well on the desk. and doesn`t move when in use ! ! ..

I understand that the key had several different types of cover made for it... consisting of mild steel, brass, and fibreglass.   As far as I know, I have the only Chromed Cover key.... I am assuming that some previous owner had it done. .The normal colour of the key would be "navy" eggshell pale blue, or pale green. as can be seen in many pics available on Google Images.

So, I removed the two small knurled nuts on the casing to reveal the key inside.....

 on my key, there is a missing part, which is a connection block, that sits behind the key at the back end.

The gap adjuster is the round black knob on the top. (If you remove the knob, be careful not to lose the "pin" that controls the gap adjuster)...

It is annotated with numbers from 0 to 9, and originally, 0 would have caused the key to be "on" all the time, so that would be the minimum gap... The rotation of the knob, increases/decreases the gap,... the position of the knob is held in place by a simple sprung "peg" underneath the cover, and locates in a slotted ring under the knob..

.(If you remove the knob, be careful not to lose the "pin" that controls the gap adjuster)...

To remove the rocker arm, only requires the slackening off, of the two screws on the main support,

and sliding the rocker arm back towards yourself.

 the spring plate has two cut outs for securing it when the screws are re-tightend.

Once removed, I noticed that the actual contact point, was worn, somewhat, so I decided I would have a go at rebuilding it using ordinary solder.... to do this, I employed the gas cooker method !. (because I don`t have a gas blow torch! ! !).....

. I set the rocker arm in my portable vice, for two reasons... firstly, to act as a heat sink, against the plastic "business end"... and secondly, just to hold the arm firmly in the gas jet to heat it up... I also used my trusty soldering iron, again, heated in the gas jet, to assist the flow of solder onto the end of the rocker..

. When I had decided there was enough solder, I removed it and cooled it under the cold tap.!.. then I carefully fixed it into the vice so that I could file the surface of the solder to level it out. and present a good level surface for the adjuster knob to make contact with..

 Some will say that the solder is too soft for the job,... but it won`t make "that" much difference, because when it wears down again, it will be a simple job to rebuild it again.

Putting it back together, was simple enough,... just making sure that the "tongues" of the spring plate were pushed home firmly, before tightening down.... then it was a matter of replacing the gap adjuster, and re-setting the spring tensioner with the allen key, before finally putting on the Chrome Cover, and doing a test piece... 

1 comment:

  1. Nice key. Wish I could find one. Thanks for the pictures and description!
    --Jay W8AIM