[Arran]

Some sets used a shield over the grid lead wire on the 1st audio/detector tube, primarily in sets that used Goat shields, or spray shield tubes, and obviously sets with double ended metal tubes, none of which made it into a Philco. I think maybe some Philco battery sets used a shielded cable on the 1H5 tubes, but I can't remember. Another weak spot, especially with double ended glass tubes, is the grid cap itself, the solder joint can go bad, even if the cap isn't loose.
Regards
Arran

[Arran]

You have to be careful with measuring some 2.5 volt AC tubes on later tube testers, quite often the heater voltage will be too low under load, even more so with #26 tubes on the 1.5 volt setting. The engineers behind some of these testers didn't take the current draw of early AC tubes into account when they were designing the testers, lighting a battery tube that runs on 50 ma is a lot different then an AC tube that draw 1.25 amps at the same voltage. If the tube filament looks dim on something like a 24A or a #47, measure the actual voltage going to the tube socket, you may be surprised.
Regards
Arran