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More newbie tube questions

So far so good with my McIntosh MC275 but I had a few more tube questions:

On power up one of the KT88 tubes and a couple of the smaller input tubes flash for a second then settle into the orange glow. All the other tubes in both amps just sort of "wake up" to the orange glow. I tried swapping the tubes and it's the socket. Whichever tube is in those sockets "flash" on power up. Nothing is wrong with the sound or performance (based upon my 6 day experience level) Should I be concerned?

Second, I ordered a complete set of Svetlana Winged C KT88 tubes. Each amp takes 4 and I received 6 with a bias point of 45 and 2 have a bias of 44. According to the McIntosh literature, the MC275 is self-biasing. Since I have NO IDEA what ANY of this means, is it a problem that 2 of the tubes are "off" by one unit? Is this the correct bias for this amp?

Last, the small output tubes say 12AX7A but all I could find are 12AX7 (no A). Is there a difference? I plan on using the Ei Grey plate tubes for these - do they have to be balanced and/or matched? I'm running both amps in mono with the RCA inputs.

On the same vein, I'm also looking to change the 12AT7 to NOS Mullards. Opinions please.

Thank you again for your help. I think this will set me up for awhile.
128x128pookie10
marakanetz's avatar
marakanetz
5,473 posts
 
Pookie,
First off how old is your amp?
pookie10's avatar
pookie10 OP
41 posts
 
Almost 6 days for the left and 4 days old for the right. They are brand new.
herman
2,274 posts
 
You are wise to read the manual and to be careful around fragile glass bottles wth high voltage inside, but the tube cage is designed to keep you from dropping things in and breaking the tubes and to keep small children and pets from falling in. Removing it for a bit so you can get a better look won't hurt a thing unless you press your nose against one of the big tubes and burn it. Put the cage back on when you are done having a look.
pookie10's avatar
pookie10 OP
41 posts
 
Yes, it's just the tubes not the socket. And it's coming from 2 of the small output tubes not the KT88s. I guess that's alright then. One problem solved. Now I have a crackling/popping in one speaker issue (same amp - maybe it's a lemon?) that cropped up after swapping around the input tubes. I can't figure out if it's the mechanical gain control, an output tube, something left-over from the pre-amp, or the speaker. Will try to isolate this weekend. Otherwise the system really is blowing me away with their liquid sound.
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