The KM64 is a pencil microphone introduced in 1966.
It was produced between the KM56 and the KM84, the first transistor microphone of this size, to my knowledge.
It uses the AC701 valve.
My KM 64s are combined with hand made capsules from Jean Marie Mallet. Their diameter is a little bigger than the Neumanns. It sounds perfect on my piano.
A big thank you to Jean Marie.