[TA Forbes]

I'm betting that it's the transformer. Of the two issues, either an H to K short in the 84 tube, or a bad power xfrm, the tube problem is not as common. However, IF the 84 does have an H to K short, I still bet the transformer caused it or went along for the ride.

Having worked on several Zs that employed the venerable 6X5 tube/tubes, that is usually the damage incurred.

Power transformers are NOT had to find for this set, be it an original OR an aftermarket replacement.

With respect to the B+ issue being caused by the 41 tube circuity, that is a logical place to check, but I would have checked the power transformer/rectifier/filter circuitry first, as that is where most B+ issues originate from..