[Amps] filament supply d.c. or a.c.

[Roy]

Asked,

"Looking for reliable information regarding filament supply to amplifier
tubes. What are the pros and cons for  D.C or  A.C volts."


Definition of 'filament' indicates a directly-heated cathode. In this case, 
using DC causes a variable voltage gradient across the length of the 
filament, acting as a variation in bias at an infinite number of points 
along its length. This has a number of ill effects. With indirectly heated 
cathodes, AC or DC is just fine.

73,   Roy    K6XK