mopardave Posted January 12, 2019 Share Posted January 12, 2019 Where do you guys bias these at? I had mine at .40ma and rebiased today to .37ma. Seems like they lost there punch a bit or is it just my imagination? The low bass is still good, but seems like the mids and highs lost their sparkle just a bit. I now find myself wanting to turn the volume up to get the same effects I once had before the rebias today. The jones bias graph shows 37ma with 485v on the plate. I don't care about longevity. Quote Link to comment Share on other sites More sharing options...
Schu Posted January 12, 2019 Share Posted January 12, 2019 If you can hear .03mA your good. I am not sure how many around here use kt77's, though I am sure they all have at one time or another. I can't help you with bias point because I only used them in conjunction with an auto-bias circuit some time ago. Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 12, 2019 Author Share Posted January 12, 2019 57 minutes ago, Schu said: If you can hear .03mA your good. I am not sure how many around here use kt77's, though I am sure they all have at one time or another. I can't help you with bias point because I only used them in conjunction with an auto-bias circuit some time ago. Not sure at this point. My ears may need a rest. Try again tomorrow. I understand these GL KT77's can take 32watt as max setting, but not sure how to figure the bias setting out of that. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted January 12, 2019 Share Posted January 12, 2019 Forgive me for asking the obvious, but wouldn’t your question be highly dependent on the amplifier that they are installed in? Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 12, 2019 Author Share Posted January 12, 2019 1 minute ago, jimjimbo said: Forgive me for asking the obvious, but wouldn’t your question be highly dependent on the amplifier that they are installed in? Not sure, but my amp is rated at 30w/ch and some say 35w/ch. Don't know much tech on these tube amps. I just want to run these tubes hot as I can to get a listen. Quote Link to comment Share on other sites More sharing options...
Schu Posted January 13, 2019 Share Posted January 13, 2019 Plate current is fairly accurate... somewhere between 70%-80% I would think is good. Perhaps an actual builder would know best. I think you are in the ballpark anywhere between 33mA and just under 40mA. You can probably run hotter, and it may sound better, but you'll shorten tube life. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted January 13, 2019 Share Posted January 13, 2019 OK, let’s try to make some progress here. First of all, what brand and model is your amp? If it is a commercially produced amp, do you have an owners manual that might suggest the bias settings? If not have you reached out to the manufacturer to ask their recommendations? Is there a technical forum for your brand of amp, and have you done any research there if so? Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted January 13, 2019 Share Posted January 13, 2019 Making recommendations simply based on the type of tube is a waste of time. Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 13, 2019 Author Share Posted January 13, 2019 2 minutes ago, jimjimbo said: OK, let’s try to make some progress here. First of all, what brand and model is your amp? If it is a commercially produced amp, do you have an owners manual that might suggest the bias settings? If not have you reached out to the manufacturer to ask their recommendations? Is there a technical forum for your brand of amp, and have you done any research there if so? Audcom AP-900a Chinese tube amp. No manual, not much out there about this amp. Had it since 2003, modded by craig@nosvalves in 2003 with Russian and aurie caps. I usually bias EL34 and KT77 at 38ma, but want to try these at max bias, what ever that may be. Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 13, 2019 Author Share Posted January 13, 2019 3 minutes ago, jimjimbo said: Making recommendations simply based on the type of tube is a waste of time. I know, too many combinations. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted January 13, 2019 Share Posted January 13, 2019 Have you talked to Craig? Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 13, 2019 Author Share Posted January 13, 2019 1 hour ago, jimjimbo said: Have you talked to Craig? Not I quite a while now. I would have to contact him thou this site. He moved from near me yrs ago to the north. Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 13, 2019 Author Share Posted January 13, 2019 19 hours ago, Schu said: If you can hear .03mA your good. I am not sure how many around here use kt77's, though I am sure they all have at one time or another. I can't help you with bias point because I only used them in conjunction with an auto-bias circuit some time ago. You were correct schu. Just hearing things. Everything sounds real nice today. Just did some spirited listening as some call it, 90-105db on the Supers. Claud did a great job figuring the Heresy's out. With the Gold Lion KT77 about 25w/CH and a Sony SACD player, these Supers are simply Bad ***. Clean clear and very punchy with the right amount of low bass. Bias at 37ma works for me. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 13, 2019 Share Posted January 13, 2019 Dave, Bias them with the lights down low so you can see at what point as you raise the bias the main plates in the tubes start to glow red. Raise them a little at a time, let the amp play for an hour before you determine if they are starting to red plate. Once they start to red plate back them down 5 points... If it sounds too tight/confined to you at that point then lower it a little more until things loosen up and sound more natural. Quote Link to comment Share on other sites More sharing options...
mopardave Posted January 13, 2019 Author Share Posted January 13, 2019 32 minutes ago, NOSValves said: Dave, Bias them with the lights down low so you can see at what point as you raise the bias the main plates in the tubes start to glow red. Raise them a little at a time, let the amp play for an hour before you determine if they are starting to red plate. Once they start to red plate back them down 5 points... If it sounds too tight/confined to you at that point then lower it a little more until things loosen up and sound more natural. Hi Craig. Good to hear from ya. Ok, will give that a try, maybe next weekend. Just giving my ears a break with some low level listening. Great advice and thanks man. Quote Link to comment Share on other sites More sharing options...
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