[R-390] R725 conversion thoughts

[Perry Sandeen]

List,

The 390 Non A IF uses series wired filaments with a voltage supply instead of a constant current type.

This may have been done for expediency without consideration of long tube life.

Yes, most filaments are almost the same resistance but not always.

The other major PITA is if you want to change one tube.......

Personally, I'd take the filament rewiring PITA so I could run the filaments at 6.0 V. per the RCA tube manual  data.  This will also allow you to mix/match different tube types for better performance.
Pick your poison?
Regards,
Perrier