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kt77 bias setting


mopardave

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Dave, I was not suggesting changing the bias.  All of our amps have various bias settings for optimal operation.  Mines is basically an EL 34 amp and the manufacture has a bias range for the EL 34 and 6CA7 printed on the top of the amp where the adjustments are done. The type of tubes that can be used for each slot is also printed in the chassis next to the tube slot.  They made it super user friendly.  

 

The KT 77 in many amps use a bias of 0.4 to 0.5.  The setting of 0.45 that you had the amp should be in the right ball park.

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Listening now. I rebias kt77 to .40 from the .45 and i think there is a small improvement in sound. Better sound stage to me.   Power transformer is now hot again and the output trans is a few degrees warmer. Sounds good to my ears. Listening to neil young freedom. What a great recording 

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  • 8 months later...
  • 3 weeks later...

Thanks Craig.   The K77's sound badass and better that the EH fatbottles I used to think were the best in this amp.   It's been awhile since i'v listened with the Home Brew Cornwalls, since i'v moved back to MM and don't have room for them now. Stored at my dads til we find a bigger home.   I still have 1 pair of Heresy's that I robbed parts from when building the CW's, but now gonna do a modification on them with new E Delta Pro 12A woofers and add a port in the rear with new Crites B xo's.      Should be a fun project.      

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I'm curious.  What's your AV line voltage read coming out of the wall outlet and what do the Mac tube amps need to see "optimally"?  I know with my VTA ST-70, the 6550 tubes need to bias around .50 per tube based on 117v recommended wall voltage.  My voltage ranges from 124 to 127v at all times so I've got a variac to dial it back to between 115 and 117v.  Otherwise, I believe it's the rectifier voltage that swings over 7v where it should be closer to 6.3v.  (I could be wrong about that)  Also, the higher the wall voltage, the more it changes the bias adjustments.  Also, my 50 year old Mac MC250 says on the front of it that it's rated at 117v and the tech yesterday said it would be best to keep it at that versus the higher amount coming from the wall.  Just a thought and observation...

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