Join Date: Nov 2003
Location: North Adams, MA
Re: legacy 50 watt setting
Pentode mode uses all 4 filaments of the tube. Triode uses only 3 which cuts the wattage down (in half, ironically!). All 4 tubes are still used in both modes.
What was cool about the 30th anniversary Marshall is it had a triode/pentode switch AND a switch to go from 2 to 4 power tubes, in effect giving us 50 or 100 watts with 4 power tubes, or 25 or 50 with only 2. That option is pretty rare though.