Mac MC240

I am kinda new at the tubes..but its funny, i find the amps as they are now, to be tremendous powerhouses throughout the freq range..again ,maybe ignorance is bliss in my case. Just cant spring for NOS tubes really.

Also,I double checked, and I dont have the RCA clear tops (differemt amps)...they are Sylvania also.

When i bought my amps, a McTech brought them up to specs. they are driving Tannoy System 12 DMTs thru a Berning TF-10 preamp/

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.