6550 replacements for upgraded CD7

Call Calvin at ARC. I am a little puzzled by your Q. I used to own the CD-7 with upgraded power supply. The upgrade involved replacing two of the three 6H30 PS tubes with one 5881 tube. I am puzzled because I'm simply not aware that one can drop-in a 6550 or KT-88 tube in exchange for the factory installed 5881 tube. Be careful.

I think he's going to tell you not to use a 6550 because it's supposed to be a 5881/6L6. That tube is used as a pass element in a voltage regulator circuit and should not be changed. @Bifwinne I believe the update was replacing 2 6H30's with one 5881 which is an industrial compact version of a 6L6 tube. Those tubes are identical and can be substituted but I think ARC uses the compact version for space requirements. The replacement/update may have had something to do with tube reliability ie. with 2 6H30's you are 2 times more likely to have one fail vs. one 5881 and they used 5881's with great success in the SP-10 preamp with no issues.

Correct Gary. Bottom line point. I would not drop in a 6550 tube in the upgraded CD-7 unless checking with the factory. It may simply be the wrong tube.