fet servo choke help needed please

[fidspeed]

I apolgise firstly because i know this will have been covered before somewhere
i have come across a couple of old ko fet servos which are still in gwo but i remember having to wire a choke into the lead fronm speedo or positive battery feed but i'm buggered if i can remember its spec

4.7 or 47 somethings or other rings a distant bell but only faintly can anyone help ?

thanks dave