A 6U5 takes - 22 volts to close. Doubt a radio can give this AVC voltage without a station being very close. If eye closing is a problem change the 6U5 to 6E5. This tubes closes with - 8 volts AVC.

Tubes can give more gain with less grid bias. If a cathode is grounded grid bias will be zero without a signal. Tubes like 6U7G were designed to operate with min bias of - 3 volts.

Norm

:Hi Mack: I'd be curious if you grounded the cathodes again and removed the 6Q7 tube if you would still see a lot of negative bias on the RF tubes. Seen where the 6A8 tube will create a large negative bias on SW band. Seen this with a Zenith 8-S-154. A gimmick capacitor was used to apply a small amount of negative feedback from the osc to the RF input of the 6A8 to eliminate the negative voltage created within the tube. The gimmick was missing on my radio. Why this can occur in 6A8 is a mystery to me.
:
:Richard