12BH7A tube in place of your 3TF7
I did this mod' several years ago and My 1967 EAC R390A serial # 5911 and it has worked with out a hitch since that day.
Ken
Kenneth A. Crips W7ITC, AMI 873
with Irish Terriers Chic' Beezie
and Cowboy. In this house Vacuum
Tubes still rule.