The variac note on the EL34 with the Mark V, we can include the same for the MWDR and Roadster (they recommend tube rectification only for EL34).
Mostly due to issues with the EL34 and their variants back in the day. Even Marshalls were having issues with the tube quality so they decided to shift to 6550 tubes instead.
Current production EL34 like the STR447 (EH EL34) or the Gold Lion KT77, EH 6CA7, Tung Sol EL34B They can tolerate the higher plate voltages without sudden death. When dealing with NOS tubes, I would consider them to be of concern. That includes the MESA NOS STR450 Siemens EL34. Tried a set of those and ended up having to ship back the TC50 after the fuse blew out and amp would not function even with the stock tubes and new fuse. (strobe mute circuit took a dive but Mesa claims it was not due to the tubes. Strobe mute will not blow the fuse but the old EL34 will as that amp runs 450V plate voltage.
In other words, the Variac power mode note on the V and the tube rectifier for the Dual Rectos is just a CYA notice. Most of the other manuals indicate if you decide to run with EL34 power tubes, have several sets available due to their shorter life span or unpredictable reliability. However, no mention of such with the TC or Badlander. However, it may explain why you get a volume drop when using 6L6 tube sin those amps.
Mostly due to issues with the EL34 and their variants back in the day. Even Marshalls were having issues with the tube quality so they decided to shift to 6550 tubes instead.
Current production EL34 like the STR447 (EH EL34) or the Gold Lion KT77, EH 6CA7, Tung Sol EL34B They can tolerate the higher plate voltages without sudden death. When dealing with NOS tubes, I would consider them to be of concern. That includes the MESA NOS STR450 Siemens EL34. Tried a set of those and ended up having to ship back the TC50 after the fuse blew out and amp would not function even with the stock tubes and new fuse. (strobe mute circuit took a dive but Mesa claims it was not due to the tubes. Strobe mute will not blow the fuse but the old EL34 will as that amp runs 450V plate voltage.
In other words, the Variac power mode note on the V and the tube rectifier for the Dual Rectos is just a CYA notice. Most of the other manuals indicate if you decide to run with EL34 power tubes, have several sets available due to their shorter life span or unpredictable reliability. However, no mention of such with the TC or Badlander. However, it may explain why you get a volume drop when using 6L6 tube sin those amps.