I have a bit although it was with a different version. Here are some tips:
The unit relies on batteries to bias the input tubes of each gain block. Replace them if their provenance is unknown. Be careful- the construction technique is a bit dodgy. It employs V-Cap coupling caps from what I've seen. They are paralleled caps of different values. You might have a tech look into that- paralleling caps in a signal path is usually a Bad Idea as it can cause smearing of the signal due to the different dissipation factors, different extended series resistance, different parasitic inductance and so on, even if the best dielectric (Teflon) is used. You're always better off with a single cap and giving it your best shot.