Hi Duka,
EF72 or 5840/CV465 are a HF subminiature wire ended pentode, some application use was in IF amplifiers around 10 mHz.
Heater: 6,3V/150mA, Anode max: 100V/7mA
Pin: 1=g1 2,8=k,g3 3=h 4=h 5=a 6=h 7=g2
I don`t have more data, but if the g1 Cg/capasitance and Rg/resistance are enough low recpective high (it should be because it is a HF tube) maybe you can use this pentode as a cathode follower and drive a output transformer around 5:1/5k-200 ohm or maybe drive a high ratio transformer from the anode.
The funny is that the mostely of tubes can be used in audio amplification circuits, ok for the condenser microphones application it is important to match the capsule to a very hi-z input (100Mohm and up) but the grids on tubes is nearly as a gate on JFET transistor, so with some luck it can be ok.
--Bo