Apparently been bitten by the bug.
A R&S UPGR Psophometer is on its way to me.
Why? I don't really need it but since I happen to have the full service manual its worth a try.
Fault description by the seller: - supply is shorted.
But battery case and meter are OK.
We will see. If the repair and full calibration goes well I'll be out hunting for an matching audio frequency generator
from the same period (ca. 1980) preferably also from R&S. Or from a different European manufacturer.