Mac MC240

Dear friends,
Thanks for all the inputs. I definitely agree with Chang's comment on the clear top RCA 12au7. I have a matched pair. It is good but all depend on which preamp you used. I don't think I have the long plate of the Mullard 12ax7 (or I may, just somewhere in my galaxy!), but I have a short plate.

Two more questions: 1. It is on the position of the power tubes. Say, the one nearest to the front panel (with the knobs and speaker wire screws) is #1 and #4 will be the one near the back. Which pair is for the right channel and which is for the left channel? If I have two matched pair (not matched quad), how should I align them? 2. What is the first 12ax7 (usually with a protection cap) used for? I can see the rest six tubes are for the right and left channels, just not sure what is the 1st one used for.

Thanks again and have a nice weekend.

1. For the output tubes, the one in front of the left transformer is left channel ( The center transformer is power transformer) the vise versa. V8 and V9 are left and V10 and V11 are right.
Since MC240 are auto-bias, it is recommend that match quad is used. If not match quad then match pair should be 2nd choice. Honestly, I couldn't tell the difference even when tubes are not matched.

2. The first 12AX7 is the input tube for both channels.

Thanks Chang.