"Reduced" sensitivity, or "no" sensitivity?
If the latter, it's almost assuredly the 6C4. You may need to try several to find one that works correctly. .......
Also look at the switches associated with switching the various IFs around. Not sure off the top of my head where the 170 switches from double to triple conversion, but that might be a start - what's different between 160/80 and the other bands.
I'd go to the switch contacts for the first two tubes, as well as the 1st mixer. My RX is a 170A VHF that had problems with noise on strong sigs...it was V12 the 6C4. At the time I had two sticks of
NOS RCA 6C4s and 7 of 10 had grid-cathode problems.
This is from feeble memory.... ~8^)=
EdZ KG6UTS