[PTurney]

Hi,

The volume control on this set is at the front end, in the antenna circuit, so no adjustment of it will reduce noise introduced in later stages of the set. Since the noise disappears when you "kill" the 2nd detector it is likely being introduced in one of the stages between antenna and (including) the 2nd detector.

Have you tried swapping out tubes, or even changing the 24s around? Tubes can generate unpleasant noises even when they test out correctly (even if caused by degraded solder connections in the base or grid cap).

In addition to the things already suggested, ensure there are no dry solder joints. Although not on a model 70 (actually a Philco 38-12), I've had noise introduced by poor connections to the little socket that pushes onto tube grid caps (what's the proper name for that??), even when the connection has looked ok. Re-solder these to be sure.

Does the noise get worse if you gently tap the chassis? Going to be a process of elimination.

Good luck!
Paul