While cleaning my Amp Supply LK 500ZC this afternoon I decided to measure
filament v. It was 4.64 on 1 tube and 4.68 on the other. Last winter I
measured them at 4.79. My voltage runs 245 or more in the winter.
The amp has the original 1987 Eimacs and I have put several thousand
hours on these tubes in the 5 years I've owned it and never babied them.
Legal limit takes about 115-120 watts drive.
Would putting 5.0v on the filaments be worth while or just wear out the