mopardave Posted March 26, 2017 Share Posted March 26, 2017 when do you guys like to bias your kt77's at? I have 470v at the plate. Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted March 26, 2017 Share Posted March 26, 2017 For my amp, the bias is set 0.35 -0.40. The 0.47 would be a bit hot but, I have never used those tubes. I say put it where it sound best! Quote Link to comment Share on other sites More sharing options...
mopardave Posted March 26, 2017 Author Share Posted March 26, 2017 Ok, had them at .40 and reset the .450 and now power and output transformers run warm. Used to run hot. Would this be normal? Maybe amp is taking a dump? Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted March 26, 2017 Share Posted March 26, 2017 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. Quote Link to comment Share on other sites More sharing options...
mopardave Posted March 26, 2017 Author Share Posted March 26, 2017 Wasn't sure,but i didn't think it sounded as good at .45 vs .40 and now the transformers don't get hot like it used to. Not sure if the bias settings could cause the issue. Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted March 26, 2017 Share Posted March 26, 2017 I think you are fine with a bias setting of 0.4-0.5. Just listen and see if things sound then near 0.4 and go up from there. If you stay in the bias range, the amp and tube life should be fine. Quote Link to comment Share on other sites More sharing options...
mopardave Posted March 27, 2017 Author Share Posted March 27, 2017 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. Quote Link to comment Share on other sites More sharing options...
mopardave Posted March 27, 2017 Author Share Posted March 27, 2017 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 Quote Link to comment Share on other sites More sharing options...
Schu Posted March 27, 2017 Share Posted March 27, 2017 Rebias it one more time... third times the charm. Quote Link to comment Share on other sites More sharing options...
mopardave Posted March 27, 2017 Author Share Posted March 27, 2017 if I do, I will try .350 just to see. Quote Link to comment Share on other sites More sharing options...
Steve. Posted December 2, 2017 Share Posted December 2, 2017 This is a great tool: http://www.vhtamp.com/products You can plug a DVM into it to calibrate it's meters. I was able to pick out a tube that deviated from its matched siblings easily.... especially good when each pair of tubes share a bias pot. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 2, 2017 Share Posted December 2, 2017 The lower the bias number the cooler the transformers should get.... lower number = less current...less current = less heat Something strange Quote Link to comment Share on other sites More sharing options...
mopardave Posted December 21, 2017 Author Share Posted December 21, 2017 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. Quote Link to comment Share on other sites More sharing options...
avguytx Posted December 22, 2017 Share Posted December 22, 2017 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... Quote Link to comment Share on other sites More sharing options...
mopardave Posted December 22, 2017 Author Share Posted December 22, 2017 Ok. Where im at now the line voltage has been 118v. It was more like 122v where i was at while adjusting bias last time. Iv moved since then. Good point made. Thanks Quote Link to comment Share on other sites More sharing options...
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