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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

Showing 3 responses by pookie10

pookie10's avatar
pookie10 OP
41 posts
 
Hi Herman,

No, it was the other amp that blew the fuse and I know why it did that. I think it may only be the small output tubes and the reflection makes one of the KT88 look like it's flashing as well. It's frankly very hard to see through the tube cage and the flash is so fast. I would take the cage off for better visuals but the manual says to never ever run the amp without the tube cages in place so I haven't tried. I'll try moving the tubes to the other amp tonight and I'll be able to see if it's the amp or the tubes. I'm 75% sure it's the tubes and what I think I'm seeing is a combination of paranoia and glass reflections.

I just ordered new output tubes: the Ei 12AX7 smooth or grey plate matched and the NOS Mullard 12AT7 all matched but not balanced. I already received my Winged C KT88 so I'll be good to swap out the Mc tubes this weekend. I also bought silicon tube dampers. I've done all I can think of to set me off on the right path.

If I've done soomething wrong, please tell me. If I haven't mentioned it already, you and others have been life savers. I can't thank you enough - REALLY THANK YOU!!!!
pookie10's avatar
pookie10 OP
41 posts
 
Almost 6 days for the left and 4 days old for the right. They are brand new.
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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