I have run every ARC 5 receiver I have on only 28VDC B+.  Have to use a set of headphones, but with a clean DC supply, feeding 28 to both filament and normal dynamotor B+ pin, they work fine.  The ARN6 RDF uses all common tubes and runs only 28 on the plates.  I have never analized the ARC 5 on 28V B+, checking sensitivity and selectivity, but just for normal comparisons, seemingly  very little difference except for audio power out..

Charlie W4MEC in NC