I found that socket on a music device produced around mid 1970s in GDR and I was wondering what kind of socket it is. Unfortunately, someone painted the whole device, including the contacts. Therefore, I plan to replace the socket with an IEC-320-C14.

Additional Information

The device is a so-called "Kofferharmonium" (kind of a very big harmonica) manufactured by "VEB Klingenthaler Harmonikawerke". This page has some more information on it. The third picture shows the electrical internals of the device. My machine has no switch or regulator, but the motor is directly connected to the socket.

There is no schematic or any other hint on / inside the device.

enter image description here enter image description here enter image description here

  • 2
    \$\begingroup\$ If you're planning to replace it, how does the answer matter other than as a matter of historic curiosity? Given the poor assembly you should probably rely only on internal details in figuring out how to connect the replacement. Also there may be a circuit diagram in the housing - albeit based on a small sample size, I believe that trend lasted longer in Soviet-bloc consumer electronics than in western ones, though the GDR may have had substantially their own traditions. \$\endgroup\$ Oct 16, 2018 at 18:03
  • \$\begingroup\$ Do you know what was attached to it? For example, was it for the power cord, or for connecting a peripheral device of some kind, or a microphone (not likely given the 250 V rating) or what? \$\endgroup\$
    – The Photon
    Oct 16, 2018 at 18:06
  • \$\begingroup\$ @ThePhoton It is for the power cord. The third picture on this page shows the internals. My device does not have any kind of regulation or switch, the motor is directly connected to the socket. \$\endgroup\$
    – Stanley F.
    Oct 16, 2018 at 18:12
  • \$\begingroup\$ Could You give us some details about a device? Manufacturer, type? \$\endgroup\$ Oct 16, 2018 at 18:27
  • 1
    \$\begingroup\$ Please edit the question to include this relevant info. Comments may be deleted when moderators clean up. \$\endgroup\$
    – The Photon
    Oct 16, 2018 at 18:34

1 Answer 1


This is KN-4A socket. Widely used in Eastern bloc countries in many types of electric equipment with a motor, mostly in sewing machines.

enter image description here

What is important - this socket is not provided for powering up motor or a whole device directly from mains. To make a full circuit you need a steering pedal and special cord. Pedal and cord looks like this (note similar plug but with two contacts):

enter image description here

Pedal controls the speed of the motor, inside of pedal there are switch, capacitor and potentiometer. Or sometimes a rheostat. Or sometimes even a couple of switches and resistors - the more You push the pedal, more resistors are just shorted and motor speed increase. Pedal is connected in series with one of the motor windings. Motor is single phase induction type.

Buying sockets and cords is not a problem, they're still in production because many people still use these (not so) old but very good sewing machines. The best solution - find the original pedal. Or find the parameters of original pedal and choose a similar sewing machine pedal.

If You omit the pedal the motor will be running constantly at full speed. Firstly, it doesn't like it. Secondly - sound from Your harmonica will be awful ;)

  • 1
    \$\begingroup\$ That's it! Thanks for the hint with the pedal. This seems to be a better solution than modifying the housing like it was done with the Harmonium on that page, I linked to. \$\endgroup\$
    – Stanley F.
    Oct 20, 2018 at 8:34

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