[Amps] 4CX1000A and 4CX250B input impedance in Class AB1 cathode driven and adjustaboe input restance

[Hsu]

Hi, I'm building  some cathode driven amplifiers   in Class AB1, anyone knows how many  input  impaedance  of 4CX1000A  and 4Cx250B?
   Another question: I noticed many amplifiers using adjuestable( variable inductor or cap) cathode input network in GG or cathode driven amplifier, few are fixed. but you know, the first,  if the tube and the configation are fixed, the input indutance should be  fixed, the second:  the input network's Q is 2 to 3 that means input network with very wide frequence range( many amplifier with common  input nest work in 18/21MHz), I think the adjust input net work  not needed.
  IMO, the fixed input network is the  best choice.But most of amplifier did not.Is it due to the tube spes  is discrete(not coherence)?
     73!Hsu