Gold grids rule.
Your 1960s OTK is less subtle in its portrayal of low level detail and the acoustic space. Less "hall" can be heard in the gentle pizzicato sections in Inoue's recording of Mahler 6th symphony, less presence and there-ness in solo lute passages from another favourite recording. Loud bits are that important fraction less nuanced, more generalised.
There's a surprising amount of difference between these 6n6 valves.
I'll post your OTK back, JP, and also send along a spare gold grid for you to play with. See what you think.
PM me your address please!