how can I fix the speed ofthe Blender/Mixer KENWOOD a701a?

You can search on here for 701 - in the search box at the top right.

There's a spark suppressor capacitor - a big-fat green resistor and a pair of contacts - give it all a good clean up - remove any dust and use fine sandpaper on the contacts - or a nail file.

Check the condition of the motor brushes and replace them if necessary. About £4 from Amazon

Eight years ago Maniac offered this....
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If this is the 701 & 701a models, then there is no triac, it's done with a mechanical govenor with bob weights on the bottom of the motor, this makes and breaks the current to the motor via a contact. This contact is on the circuit board that the dial moves up or down to adjust the speed. Look closely and you should see two long thin screws with springs that hold this board in position. Adjustment of these sorts out the speed. See which way the dial moves the board when you turn it to max, adjust the screws the opposite way. If you are cunning you dont need to take it apart as these screws are accessable from underneath. 1960's electrical standards apply, lots of 240 volts just waiting for the careless, so adjust only when unplugged from the national grid. Darwin Award awaits otherwise.
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e-Bay currently have a repair kit for over £20 - an expensive option - likely that you may need to replace the capacitor - very cheap from a hobby electronics shop but you may well need to have access to a soldering iron - not sure...

Do the brushes & the capacitor - clean the contacts

Good luck...
December 2014