FER have including the gas stabilizer 11 tubes,
there are 3 pcs E1T counting tubes, a 150-OB2, the input amplifier is a EF800, and 6 pcs E90CC.
in rmorg are 2 FER registered, the one is from my friend Harald, and the second is this one. They are very rare today.
I think they was in use to do long time countings from geiger mueller tubes in nuclear plants (radiation related to a longer time).
Also there is a input for a light sensitivity sensor, for shure they mean a tube in that time, I will build one, 90 CG or like that
greetings
Martin