challenge: What is the difference in sound characteristics between Ampeg SVT amps with 6146B tubes and those with 6550A tubes?
  
  A. SVTs with 6146B tubes produce a rounder, deeper bass sound
  B. SVTs with 6146B tubes tend to have a more pronounced grind in low mids and a bit more power
  C. SVTs with 6146B tubes produce a cleaner, more transparent sound
  D. SVTs with 6550A tubes have a more pronounced grind in low mids
  Answer: 